U.S. patent number 10,378,120 [Application Number 14/353,164] was granted by the patent office on 2019-08-13 for method for coating metallic surfaces with a multi-component aqueous composition.
This patent grant is currently assigned to Chemetall GmbH. The grantee listed for this patent is Chemetall GmbH. Invention is credited to Michael Droge, Thomas Kolberg, Carola Komp, Peter Schubach, Manfred Walter.
United States Patent |
10,378,120 |
Kolberg , et al. |
August 13, 2019 |
Method for coating metallic surfaces with a multi-component aqueous
composition
Abstract
A method for coating metallic surfaces with aqueous
compositions, wherein a silane-based aqueous composition containing
at least one silane and/or a related silicon-containing compound
and optionally additional components is treated further, for
example, at temperatures above 70.degree. C., in a pretreatment
step without drying the coating, by using at least one aqueous
rinse step after this pretreatment step and then performing an
electrodeposition coating, in which at least one surfactant is
added at least in the last rinse step of the aqueous rinse steps.
Coated metallic surfaces are also described.
Inventors: |
Kolberg; Thomas (Heppenheim,
DE), Schubach; Peter (Nidderau/Windecken,
DE), Walter; Manfred (Hanau, DE), Komp;
Carola (Morfelden-Walldorf, DE), Droge; Michael
(Frankfurt am Main, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Chemetall GmbH |
Frankfurt am Main |
N/A |
DE |
|
|
Assignee: |
Chemetall GmbH (Frankfurt am
Main, DE)
|
Family
ID: |
47049176 |
Appl.
No.: |
14/353,164 |
Filed: |
October 23, 2012 |
PCT
Filed: |
October 23, 2012 |
PCT No.: |
PCT/EP2012/070929 |
371(c)(1),(2),(4) Date: |
April 21, 2014 |
PCT
Pub. No.: |
WO2013/060662 |
PCT
Pub. Date: |
May 02, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20140255706 A1 |
Sep 11, 2014 |
|
Foreign Application Priority Data
|
|
|
|
|
Oct 24, 2011 [DE] |
|
|
10 2011 085 091 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D
13/20 (20130101); C25D 5/44 (20130101); C23C
22/80 (20130101); C25D 5/36 (20130101); C23C
18/1241 (20130101); C23C 22/78 (20130101); C23C
18/122 (20130101); C23C 22/83 (20130101); C25D
5/34 (20130101); C23C 22/34 (20130101); Y10T
428/31663 (20150401); C23C 2222/20 (20130101) |
Current International
Class: |
C25D
5/34 (20060101); C23C 18/12 (20060101); C23C
22/83 (20060101); C23C 22/34 (20060101); C23C
22/80 (20060101); C23C 22/78 (20060101); C25D
13/20 (20060101); C25D 5/44 (20060101); C25D
5/36 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2017327 |
|
Jan 1971 |
|
DE |
|
10 2005 015 576 |
|
Oct 2006 |
|
DE |
|
61-291997 |
|
Dec 1986 |
|
JP |
|
10-046393 |
|
Feb 1998 |
|
JP |
|
2006/050915 |
|
May 2006 |
|
WO |
|
2011/098322 |
|
Aug 2011 |
|
WO |
|
Primary Examiner: Cohen; Brian W
Attorney, Agent or Firm: Armstrong Teasdale LLP
Claims
The invention claimed is:
1. A method for improving the throwing power of an
electrodeposition coating, the method comprising: applying to a
metallic surface two aqueous treatment compositions having
different contents of at least one iron compound dissolved in water
prior to contacting the metallic surface with an aqueous
silane-based pretreatment composition; contacting the metallic
surface with the aqueous silane-based pretreatment composition that
comprises: a) at least one compound selected from silanes,
silanols, siloxanes, and polysiloxanes, of which at least one of
these compounds is still condensable, and b) at least one titanium,
hafnium, and zirconium compound, and c) at least one type of cation
selected from cations of metals of Groups IB to IIIB and VB to
VIIIB, including lanthanides, and of main group II, of the periodic
table of the elements, and/or at least one corresponding compound
c), and/or d) at least one organic compound selected from monomers,
oligomers, polymers, copolymers, and block copolymers, and e)
water, and optionally at least one organic solvent and/or at least
one substance to adjust the pH, thereby forming a pretreatment
coating; rinsing the pretreatment coating at least once with water
optionally comprising a surfactant; and applying an
electrodeposition coating after the rinsing, wherein the aqueous
silane-based pretreatment composition has a pH of from 1.5 to 9,
and wherein the pretreatment coating is not completely dried, so
that the at least one compound a) is not highly condensed before
the rinsing of the pretreatment coating with water and/or before
the coating with the electrodeposition coating.
2. A method according to claim 1, further comprising applying an
after-rinse solution following the application of the aqueous
silane-based pretreatment composition to form a second conversion
layer or a coating.
3. A method according to claim 1, wherein the aqueous silane-based
pretreatment composition has a content of silane, silanol,
siloxane, and polysiloxane in the range of 0.005 to 80 g/L,
calculated on the basis of the corresponding silanols.
4. A method according to claim 1, wherein the aqueous silane-based
pretreatment composition contains at least one silane, silanol,
siloxane, and/or polysiloxane which contains at least one amino
group, urea group, and/or ureido group.
5. A method according to claim 1, wherein the aqueous silane-based
pretreatment composition has a content of compounds of b) selected
from titanium, hafnium, and zirconium in the range of 0.01 to 50
g/L, calculated as the sum of the corresponding metals.
6. A method according to claim 5, wherein the aqueous silane-based
pretreatment composition has at least one complex fluoride of
titanium, hafnium, and/or zirconium.
7. A method according to claim 6, wherein the complex fluoride(s)
of titanium, hafnium, and/or zirconium is in the range of 0.01 to
100 g/L, calculated as the sum of the corresponding metal complex
fluorides calculated as MeF.sub.6.
8. A method according to claim 1, wherein the at least one type of
cation c) is selected from cations of aluminum, iron, calcium,
cobalt, copper, magnesium, manganese, molybdenum, nickel, niobium,
tantalum, yttrium, zinc, tin, cerium and other lanthanides.
9. A method according to claim 1, wherein in the aqueous
silane-based pretreatment composition, only types of cations or
corresponding compounds c) selected from the group of aluminum,
magnesium, calcium, yttrium, lanthanum, cerium, manganese, iron,
cobalt, copper, tin, and zinc, or selected from the group of
aluminum, magnesium, calcium, yttrium, lanthanum, cerium, vanadium,
molybdenum, tungsten, manganese, iron, cobalt, copper, bismuth,
tin, and zinc are present.
10. A method according to claim 1, wherein the aqueous silane-based
pretreatment composition has a cation content from compounds c) in
the range of 0.01 to 20 g/L, calculated as the sum of the
metals.
11. A method according to claim 1, wherein organic compounds d)
have a content in the range of 0.01 to 200 g/L, calculated as the
sum of the corresponding compounds.
12. A method according to claim 1, wherein a mix of various
metallic materials is coated with the aqueous silane-based
pretreatment composition simultaneously.
13. A method according to claim 1, wherein the aqueous silane-based
pretreatment composition forms a coating having a layer weight
which, based on titanium and/or zirconium, is in the range of 1 to
200 mg/m.sup.2.
14. A method according to claim 1, wherein the coating formed from
the aqueous silane-based pretreatment composition has a layer
weight which, based only on siloxanes/polysiloxanes, is in the
range of 0.2 to 1000 mg/m.sup.2, calculated as the corresponding
polysiloxane.
15. A method according to claim 1, wherein prior to applying the
aqueous silane-based pretreatment coating, a prerinse and/or a
first silane coating aqueous composition is performed, wherein the
first silane coating aqueous composition contains at least one
silane, at least one compound selected from fluoride-free compounds
of titanium, hafnium, zirconium, aluminum, and boron, at least one
alkaline solution, and/or at least one complex fluoride.
16. A method according to claim 1, wherein the rinse water has at
least two different surfactants which in combination improve the
wetting and foam suppressant properties.
17. A method according to claim 1, wherein at least one rinse with
an aqueous composition contains at least one surfactant for
homogenizing the wet film.
18. A method according to claim 1, further comprising applying,
after the electrodeposition coating, at least one primer, paint, or
adhesive, and/or a paint-like organic composition, to form at least
one further coating.
19. A method according to claim 1, wherein each aqueous treatment
composition having at least one iron compound dissolved in water
also has at least one complexing agent.
20. A method according to claim 1 wherein each aqueous treatment
composition having at least one iron compound dissolved in water
has a pH of 9 to 14.
21. A method according to claim 1 wherein each aqueous treatment
composition having at least one iron compound dissolved in water
has a total iron content in the range of 0.005 to 1 g/L.
22. A method according to claim 1 wherein each aqueous treatment
composition having at least one iron compound dissolved in water
contains gluconate and/or heptonate.
Description
This application is a .sctn. 371 of International Application No.
PCT/EP2012/070929 filed Oct. 23, 2012, and claims priority from
German Patent Application No. 10 2011 085 091.0 filed Oct. 24,
2011.
A method for improving the throwing power of an electrodeposition
coating by coating metallic surfaces with aqueous pretreatment
compositions is described.
The invention relates to a method for coating metallic surfaces
with aqueous compositions, wherein a silane-based aqueous
composition containing at least one silane and/or a related
silicon-containing compound and optionally additional components is
treated further, for example, at temperatures above 70.degree. C.,
in a pretreatment step without drying the coating, by using at
least one aqueous rinse step after this pretreatment step and then
performing an electrodeposition coating, in which at least one
surfactant is added at least in the last rinse step of the aqueous
rinse steps.
Previously, the most commonly used methods for treating metallic
surfaces, in particular parts, coil or coil sections made of at
least one metallic material and/or for pretreatment of metallic
surfaces before painting of the metallic surfaces have often been
based on the use of chromium(VI) compounds, on the one hand,
optionally together with various additives, or phosphates, on the
other hand, for example, zinc-manganese-nickel phosphates,
optionally together with various additives.
For many years now, there has been a search for alternatives to
these methods in all the fields of surface technology for metal
substrates because of the toxicological and ecological risks
associated with methods using chromate or nickel in particular, but
it has nevertheless been found repeatedly that in many
applications, completely chromate-free or nickel-free processes do
not fulfill 100% of the performance spectrum or not with the
desired certainty. Then an attempt is made to keep the chromate
content and/or nickel content as low as possible, to replace
Cr.sup.6+ with Cr.sup.3+ as much as possible. High-quality
phosphating treatments, which have kept corrosion protection of
automobiles at a high quality level, are in use in the automobile
industry in particular, for example, for pretreatment of vehicle
bodies before painting. Zinc-manganese-nickel phosphating
treatments are usually used for this purpose. Despite many years of
research and development, it has not yet been possible to develop
methods for phosphating treatment for multimetal applications
without the use of nickel and without any definite quality
restrictions, as in the case of vehicle bodies, for example. In
Europe, metallic surfaces of steel, galvanized steel and aluminum
and/or aluminum alloys are typically treated in the same bath. In
the foreseeable future, however, the nickel content, even if it is
comparatively low, will have to be classified as more objectionable
toxicologically, so the question arises as to whether equivalent
corrosion protection can be achieved with other chemical
processes.
In the automobile industry in particular, an electrodeposition
coating using an electrodeposition paint, such as a cathodic
electro-dip coating (CDC) is often used as the first paint layer in
the automobile industry in particular. The compositions and use
conditions in electrodeposition coating are fundamentally
known.
The use of silanes/silanols, for example, in aqueous compositions
to produce siloxane/polysiloxane-rich anticorrosion coatings is
fundamentally known. For the sake of simplicity, when silane is
mentioned below, it is understood to refer to
silane/silanol/siloxane/polysiloxane. These coatings have proven
successful, but the processes for coating with an aqueous
composition containing primarily silane plus solvent(s) have proven
to be difficult to use in some cases. These coatings are not always
formed with excellent properties. Furthermore, there may be
problems in being able to adequately characterize the very thin
transparent silane coatings on the metallic substrate and their
defects with the naked eye or with optical aids. The corrosion
protection and the paint adhesion of the resulting siloxane-rich
and/or polysiloxane-rich coatings are often, but not always, high
and to some extent are not high enough for certain applications,
even when applied suitably. Additional processes using at least one
silane are needed to achieve high process reliability and a high
quality of the coatings produced with them, in particular with
regard to corrosion resistance and paint adhesion.
In the design of silane-based aqueous compositions, a small and/or
large added quantity of at least one component selected from the
group of organic monomers, oligomers and polymers has also proven
successful. With such compositions, the type and quantity of silane
added is of crucial importance for their success in some cases.
However, the amounts of silane added for this purpose are usually
comparatively low--in most cases only up to 5% by weight of the
total solids contents--and then act as a "coupling agent," wherein
the adhesion-promoting effect should prevail in particular between
the metallic substrate and the paint and optionally between the
pigment and the organic paint constituents, but a minor
crosslinking effect may also occur to a lesser extent. Primarily
very small amounts of silane additives are added to thermally
curable resin systems.
When using silane-based solutions for coating metallic surfaces, it
has been known in the past that solutions containing essentially or
mainly silane and its derivatives are sensitive to water if the
coatings have not been dried to a greater extent, so that a water
rinsing of the freshly applied coatings, which have not yet dried
thoroughly, will usually result in an impairment of the coatings,
e.g., due to separation, because they are not sufficiently
rinse-fast. Evidently the very thin oxide/hydroxide layers of the
"natural" oxide films on metallic surfaces are not sufficient to
adequately keep freshly applied silane adhering before it is dried
thoroughly. These coatings are usually insensitive to water only
when the coatings have been dried (for example, for 5 minutes at
80.degree. C. PMT (peak metal temperature), e.g., 25 minutes at
70.degree. C. PMT or higher) because condensation of the
silanes/silanols/siloxanes/polysiloxanes will have already
progressed to a greater extent. The degree of drying which is
associated with condensation of the
silanes/silanols/siloxanes/polysiloxanes and leads to a
rinse-fastness of the siloxane/polysiloxane-containing coating is
variable, depending on the phase, the coating and the type of
rinsing.
Existing phosphating plants, in particular in the automotive
industry, for cleaning and pretreatment of vehicle bodies before
painting, for example, do not require a drying installation.
However, such a channel-type installation is often more than 100
meters long even without such a drying installation. In many cases,
such an installation is located in immediate proximity to an
installation for coating by cathodic dip coating (CDC) at the end,
where the completely phosphate vehicle bodies emerge from the
channel, so that in most cases no room is available for the
incorporation of a drying plant in addition.
When using electrodeposition coating after a silane-based
pretreatment, there has been the problem in automotive engineering
in particular of reducing the voltage of the electrodeposition
coating in comparison with a process sequence that includes a zinc
phosphate coating, because the comparatively thick zinc phosphate
layers result in a much higher electric resistance in the
electrodeposition bath. Due to the use of lower electric voltages
in the electrodeposition bath with a comparatively thin
silane-based pretreatment coating with a comparatively low electric
resistance, there may be problems with evenness, uniformity and
visual appearance of the applied electrodeposition coating as well
as the throwing power of the paint, especially on undercut
locations of metal parts having a complex shape.
When using electrodeposition coating after a silane-based
pretreatment, there has been the problem of improving the quality
of the electrodeposition coating in automotive engineering in
particular, because in many situations the throwing power is
inadequate in the case of workpieces and constructions with complex
shapes such as housings and vehicle bodies, for example, to permit
the most uniform possible layer thicknesses of the
electrodeposition coating on the inside and outside and thereby
also fulfill all the other quality requirements of the coating.
The object was therefore to propose a method for aqueous
compositions whose coatings would have the most environmentally
friendly chemical composition possible while ensuring a high
corrosion resistance, which will be suitable even in multimetal
applications in which, for example, steel and zinc-rich metallic
surfaces and optionally also aluminum-rich metallic surfaces are
treated or pretreated in the same bath. Another object was to
propose a process sequence from pretreatment to electrodeposition
coating in which high-quality coatings of the silane-based
pretreatment and electrodeposition coating can be applied to
vehicle bodies in mass production of automobiles with as little
trouble as possible. Furthermore, another object was to propose a
method using silane-based aqueous compositions that could
fundamentally be implemented in existing plants in the automotive
industry and would be suitable for coating vehicle bodies in
automotive engineering in particular. A quality coating of
pretreatment coating and electrodeposition coating on vehicle body
surfaces is to be achieved here, such as that achieved with
high-quality anticorrosion coatings in zinc-manganese-nickel
phosphating treatments, so as not to endanger the quality
standard.
It has now been found that adding at least one surfactant in the
one rinse step in rinsing with water after the silane-based
pretreatment or at least in the last of several rinse steps in
rinsing with water after the silane-based treatment makes it
possible to achieve a uniform electrodeposition coating, such that
there is better throwing power of the electrodeposition paint and
possibly also of the electric field in electrodeposition coating
and the layer thicknesses of the electrodeposition coatings are
significantly more uniform from the outside to the inside, for
example, in the case of a housing or a vehicle body.
The addition of complex fluoride in the silane-based pretreatment
helps to minimize and/or prevent impairment of the binding of
silane to the metallic surface, so that rinsing can have little or
no harmful effect. A combination of at least two complex fluorides
in the silane-based pretreatment composition, in particular
fluorotitanic acid and fluorozirconic acid and/or their salts, also
permits an extraordinary increase in the quality of the
coatings.
It has been found that it is not only possible to rinse freshly
applied coatings, which are not yet fully dried and therefore have
not yet undergone a higher degree of condensation in the case of
coatings based on silane, but this process sequence is instead even
advantageous because the pretreatment coatings produced and rinsed
in this way have an even better anticorrosion effect and better
paint adhesion, regardless of the chemical composition of the
aqueous silane-based (=silane/silanol/siloxane/polysiloxane and/or
silane/silanol/siloxane) pretreatment composition to some extent.
This is in contradiction with previous experience, according to
which rinsing of a freshly applied, not yet thoroughly dried
coating based on silane often has a negative effect on the quality
of the layer, if not partially, or in some cases even completely,
removing the coating.
It has also been found that it is possible and advantageous to
apply a paint such as an electrodeposition coating paint, a
paint-like coating, a primer or an adhesive to freshly applied
silane-based pretreatment coatings which have not yet dried
completely and therefore have not yet fully condensed, but which
have optionally also been rinsed in this condition. The application
of such compositions to silane-based wet films is advantageous
because the coatings produced and rinsed in this way even have a
better anticorrosion effect and better paint adhesion in some
cases, regardless of the chemical composition of the aqueous
bath.
It has now been found that the use of an aqueous composition
containing iron prior to applying the silane-based pretreatment
composition permits an increased voltage to be used in
electrodeposition coating. The voltage used here may often be 5% to
15% higher. It has been found here that the throwing power thereby
obtained is improved by approx. 5% to 15% because of the higher
voltage.
This object has been achieved with a method for improving the
throwing power of an electrodeposition coating by coating metallic
surfaces with a pretreatment composition containing
silane/silanol/siloxane/polysiloxane, this composition also
containing the following in addition to water and optionally in
addition to at least one organic solvent and/or at least one
substance to influence the pH: a) at least one compound a) selected
from silanes, silanols, siloxanes and polysiloxanes, wherein at
least one of these compounds may still condense, and b) at least
one compound b) containing titanium, hafnium and/or zirconium as
well as c) at least one type of cation c) selected from cations of
metals of auxiliary groups I to III and V to VIII, including
lanthanides, as well as main group II of the periodic system of
elements and/or at least one corresponding compound c) and/or d) at
least one organic compound d) selected from monomers, oligomers,
polymers, copolymers and block copolymers, wherein the coating
freshly applied with this composition is rinsed at least once with
water, wherein at least one water rinse contains a surfactant,
wherein an electrodeposition coating is applied after rinsing with
water, and wherein the coating freshly applied with this
composition is not dried thoroughly before this rinsing, so that
the at least one condensable compound a) is not highly condensed
before rinsing the pretreatment coating with water and/or before
coating with an electrodeposition paint and/or wherein the
pretreatment coating applied freshly with the pretreatment
composition is not dried thoroughly before applying a subsequent
electrodeposition coating, so that the at least one condensable
compound a) is not highly condensed before the subsequent
electrodeposition coating is applied.
The object of the present invention is also achieved with a method
for improving the throwing power of an electrodeposition coating by
coating metallic surfaces with a pretreatment composition
containing silane/silanol/siloxane/polysiloxane, characterized in
that this composition contains the following, in addition to water
and optionally in addition to at least one organic solvent and/or
at least one substance to influence the pH: a) at least one
compound a) selected from silanes, silanols, siloxanes and
polysiloxanes, where at least one of these compounds can still
condense further, and b) at least one compound b) containing
titanium, hafnium and/or zirconium as well as c) at least one type
of cation c) selected from cations of metals of auxiliary groups I
to III and V to VIII, including lanthanides, as well as main group
II of the periodic system of elements and/or at least one
corresponding compound c) and/or d) at least one organic compound
d) selected from monomers, oligomers, polymers, copolymers and
block copolymers, wherein the coating applied freshly with the
pretreatment composition is rinsed at least once with water,
wherein optionally at least one water rinsing has a surfactant
content, and wherein an electrodeposition coating is applied after
rinsing with water, wherein the coating freshly applied with this
composition is not dried thoroughly before this rinsing, so that
the at least one condensable compound a) is not greatly condensed
before rinsing the pretreatment coating with water and/or before
coating with an electrodeposition coating and/or wherein the
pretreatment coating freshly applied with the pretreatment
composition is not dried thoroughly before applying a subsequent
electrodeposition coating, so that the at least one condensable
compound a) is not highly condensed before applying the subsequent
electrodeposition coating, and wherein an aqueous treatment with a
water-dissolved iron compound content is performed before the
treatment with an aqueous silane-based pretreatment
composition.
This object is also achieved by using an aqueous silane-based
pretreatment composition in a coating method for metallic
substrates for improving the throwing power of an electrodeposition
coating, in which an aqueous silane-based composition is brought in
contact with a metallic substrate, wherein the coating applied
freshly with this composition is rinsed at least once with water,
wherein the rinsing is performed at least once with water
containing a surfactant, in which an electrodeposition coating is
applied after rinsing with water, and the coating applied freshly
with this composition is not dried thoroughly before this rinsing,
so that the at least one condensable compound a) does not condense
to a great extent before rinsing the pretreatment coating with
water and/or before coating with an electrodeposition paint.
Finally, this object is achieved with the use of an aqueous
silane-based pretreatment composition in a coating method for
metallic substrates for improving the throwing power of an
electrodeposition coating, wherein the substrates are brought in
contact at least once with an aqueous composition containing iron
before the aqueous silane-based pretreatment, wherein an aqueous
silane-based composition is brought in contact with a metallic
substrate, wherein the coating applied freshly with this
composition is rinsed at least once with water, wherein optionally
the rinsing is performed at least once with water containing a
surfactant, wherein after rinsing with water an electrodeposition
coating is applied, wherein the pretreatment coating applied
freshly with the pretreatment composition is not dried thoroughly
before applying a subsequent electrodeposition coating, so that the
at least one condensable compound a) does not condense to a great
extent before applying the subsequent electrodeposition
coating.
In one embodiment, a second conversion layer and/or a coating may
also be used in the middle of this process sequence as a result of
application of an after-rinse solution. The second conversion layer
or the coating due to application of an after-rinse solution is
preferably an aqueous composition based on at least one
silane/silanol/siloxane/polysiloxane, of at least one compound
containing titanium, hafnium, zirconium, aluminum and/or boron such
as, for example, at least one complex fluoride, at least one
organic compound selected from monomers, oligomers, polymers,
copolymers and block copolymers and/or at least one compound
containing phosphorus and oxygen. In many embodiment variants, the
concentration of the aqueous composition for the second conversion
layer and/or the after-rinse solution is lower on the whole than a
comparable aqueous composition for the first conversion layer,
namely the silane-based pretreatment coating according to the
invention.
It is particularly advantageous when the freshly applied coating is
rinsed first with water or with an aqueous solution before a
subsequent coating is applied. The wet film of the silane-based
pretreatment according to the invention may be rinsed here with
water and/or with an aqueous composition optionally containing a
surfactant without prior greater drying of the wet film with water.
Then without having dried the film to a greater extent, a
subsequent coating is applied to this wet film. The wet film is
then rinsed after the silane pretreatment, preferably immediately
after the coating with the aqueous composition containing silane,
in particular within one or two minutes after coating with the
silane pretreatment according to the invention, especially
preferably within 30 seconds or even within 10 seconds after this
coating. If several water rinses are used, it is preferable for at
least the last of these water rinses to contain at least one
surfactant. The electrodeposition paint is preferably applied
immediately after rinsing, in particular within two or three
minutes after rinsing the silane-based pretreatment coating,
especially preferably within 60 seconds or even within 20 seconds.
The paint here may be in particular an electrodeposition paint or a
water-based wet paint. On the other hand, it may frequently happen,
in particular in industrial manufacturing, that the period of time
from the end of rinsing with water until applying the
electrodeposition coating is 1 to 120 minutes, but preferably only
2 to 60 minutes or 3 to 40 minutes or 4 to 20 minutes, because it
is advantageous if, despite this waiting time, greater drying of
the rinsed silane-based pretreatment coating does not occur. It may
be advantageous here to take measures, so that the rinsed
silane-based pretreatment coatings do not dry out thoroughly and
preferably do not even dry out to a greater extent, for example,
through the use of a wettening system such as nozzles for spraying
a water mist, for example.
It is assumed that the at least one silane/silanol/siloxane that is
still condensable is still highly reactive chemically and can react
more intensely with the electrodeposition paint applied
subsequently than a silane/silanol/siloxane/polysiloxane that is
already thoroughly dried and highly condensed under the influence
of temperature. It is assumed that it will still be reactive after
a waiting period of up to several hours after rinsing, as long as a
temperature of more than 40.degree. C., for example, is not
employed, which would lead to a thorough drying of the silane-based
pretreatment coating.
The term "silane" is used here to stand for silanes, silanols,
siloxanes, polysiloxanes and their reaction products and/or
derivatives which are often "silane" mixtures. The term "condense"
in the sense of this patent application refers to all forms of
crosslinking, further crosslinking and further chemical reactions
of the silanes/silanols/siloxanes/polysiloxanes. Addition in the
form of a silane is usually assumed here, where the at least one
silane added is often at least partially hydrolyzed, usually
forming at least one silanol on initial contact with water or
humidity, at least one siloxane being formed from the silanol and
later optionally also at least one polysiloxane (possibly) being
formed. The term "coating" in the sense of the patent application
relates to the coating formed with the aqueous composition
including the wet film, the partially dried film, the thoroughly
dried film, the film dried at an elevated temperature and the film
further crosslinked, optionally by thermal and/or radiation
treatment.
The aqueous silane-based pretreatment composition is an aqueous
solution, an aqueous dispersion and/or an emulsion. Its pH is
preferably greater than 1.5 and less than 9, especially preferably
in the range of 2 to 7, most especially preferably in the range of
2.5 to 6.5, in particular in the range of 3 to 6. At a high pH of
2.5, for example, a greatly reduced separation of titanium and/or
zirconium compounds may occur, for example, from the complex
fluoride, which may have effects due to a slight reduction in the
layer properties. At a pH of approx. 7, the complex fluoride
present in the bath may become unstable and may form
precipitates.
At least one silane and/or at least one corresponding compound with
at least one amino group, with at least one urea group and/or with
at least one ureido group (imino group) is especially preferably
added to the aqueous silane-based pretreatment composition because
the coatings produced in this way often have a greater paint
adhesion and/or a higher affinity for the following
electrodeposition coating. In particular in use of at least one
silane and/or at least one corresponding compound with at least one
such group, it is important to note that condensation may proceed
very rapidly at a pH of less than 2. The amount of aminosilanes,
ureidosilanes and/or silanes with at least one urea group and/or
corresponding silanols, siloxanes and polysiloxanes in the total of
all types of compounds, selected from silanes, silanols, siloxanes
and polysiloxanes, may be elevated, especially preferably more than
20% by weight, more than 30% or more than 40% by weight, calculated
as the corresponding silanols, most especially preferably more than
50%, more than 60%, more than 70% or more than 80% by weight and
optionally even up to 90% by weight, up to 95% or up to 100% by
weight.
The aqueous silane-based pretreatment composition preferably has a
silane/silanol/siloxane/polysiloxane content a) in the range of
0.005 to 80 g/L, calculated on the basis of the corresponding
silanols. This content is especially preferably in the range of
0.01 to 30 g/L, most especially preferably in the range of 0.02 to
12 g/L, up to 8 g/L or up to 5 g/L, in particular in the range of
0.05 to 3 g/L or in the range of 0.08 to 2 g/L or up to 1 g/L.
These content ranges refer to bath compositions in particular.
However, if a concentrate is used to prepare a corresponding bath
composition, in particular by diluting with water and optionally
adding at least one additional substance, it is advisable to keep a
concentrate A, which contains silane/silanol/siloxane/polysiloxane
a) separately from a concentrate B, which contains all or almost
all the other components and not to combine these components until
they are in the bath. Optionally at least one silane, silanol,
siloxane and/or polysiloxane may also be present partially or
entirely in solid form, added in solid form and/or added as a
dispersion or solution. However, the concentration ranges of the
bath may also emphasize different contents, depending on the
application.
The aqueous silane-based pretreatment composition especially
preferably contains at least one silane, silanol, siloxane and/or
polysiloxane a), each with at least one group selected from
acrylate groups, amino groups, succinic acid and hydride groups,
carboxyl groups, epoxy groups, glycidoxy groups, hydroxy groups,
ureido groups (imino groups), isocyanato groups, methacrylate
groups and/or urea groups per molecule, wherein aminoalkyl groups,
alkylaminoalkyl groups and/or alkylamino groups may also occur.
This composition especially preferably contains at least one
silane, silanol, siloxane and/or polysiloxane a) with at least two
amino groups, with at least three amino groups, with at least four
amino groups, with at least five amino groups and/or with at least
six amino groups per molecule.
The silanes, silanols, siloxanes and/or polysiloxanes in the
aqueous silane-based pretreatment composition or at least their
compounds added initially to the aqueous composition or at least
some of them are preferably water-soluble. The silanes in the sense
of this patent application are regarded as being water soluble if
they have a water solubility of at least 0.05 g/L, preferably at
least 0.1 g/L, especially preferably at least 0.2 g/L or at least
0.3 g/L, in general at room temperature in the composition
containing silane, silanol, siloxane and/or polysiloxane. This does
not mean that each individual one of these silanes must have this
minimum solubility but rather that these minimum values are
achieved on the average.
Preferably at least one silane, silanol, siloxane, polysiloxane is
present in the aqueous silane-based pretreatment composition,
selected from fluorine-free silanes and the corresponding silanols,
siloxanes, polysiloxanes, each from at least one acyloxy silane, an
alkoxysilane, a silane having at least one amino group such as an
aminoalkyl silane, a silane having at least one succinic acid group
and/or succinic anhydride group, a bis(silyl)silane, a silane
having at least one epoxy group such as a glycidoxy silane, a
(meth)acrylate silane, a multisilyl silane, a ureido silane, a
vinyl silane and/or at least one silanol and/or at least one
siloxane and/or polysiloxane of a corresponding chemical
composition, such as that of the silanes described above. It
contains at least one silane and/or (respectively) at least one
monomeric, dimeric, oligomeric and/or polymeric silanol and/or
(respectively) at least one monomeric, dimeric, oligomeric and/or
polymeric siloxane, wherein oligomers as referenced below should
also include dimers and trimers. The at least one silane and/or the
corresponding silanol/siloxane/polysiloxane especially preferably
has at least one amino group, urea group and/or ureido group.
In particular at least one silane and/or at least one corresponding
silanol/siloxane/polysiloxane is present herein and/or initially
added, selected from the group and/or based on
(3,4-epoxyalkyl)trialkoxysilane,
(3,4-epoxycycloalkyl)alkyltrialkoxysilane,
3-acryloxyalkyltrialkoxysilane, 3-glycidoxyalkyltrialkoxysilane,
3-methacryloxyalkyltrialkoxysilane, 3-(trialkoxysilyl)alkylsuccinic
acid silane, 4-aminodialkylalkyltrialkoxysilane,
4-aminodialkylalkylalkyldialkoxysilane,
aminoalkylaminoalkyltrialkoxysilane,
aminoalkylaminoalkylalkyldialkoxysilane, aminoalkyltrialkoxysilane,
bis(trialkoxysilylalkyl)amine, bis(trialkoxysilyl)ethane,
.gamma.-acryloxyalkyltrialkoxysilane,
.gamma.-aminoalkyltrialkoxysilane,
.gamma.-methacryloxyalkyltrialkoxysilane,
(.gamma.-trialkoxysilylalkyl)dialkylenetriamine,
.gamma.-ureidoalkyltrialkoxysilane,
N-2-aminoalkyl-3-aminopropyltrialkoxysilane,
N-(3-trialkoxysilylalkyl)alkylenediamine,
N-alkylaminoisoalkyltrialkoxysilane,
N-(aminoalkyl)aminoalkylalkyldialkoxysilane,
N-.beta.-(aminoalkyl)-.gamma.-aminoalkyltrialkoxysilane,
N-(.gamma.-trialkoxysilylalkyl)dialkylenetriamine,
N-phenylaminoalkyltrialkoxysilane,
poly(aminoalkyl)alkyldialkoxysilane, tris(3-trialkoxysilyl)alkyl
isocyanurate, ureidoalkyltrialkoxysilane and vinyl
acetoxysilane.
This preferably includes at least one silane and/or at least one
corresponding silanol/siloxane/polysiloxane and/or added initially
and selected from the group of or based on:
(3,4-epoxybutyl)triethoxysilane, (3,4-epoxybutyl)trimethoxysilane,
(3,4-epoxycyclohexyl)propyltriethoxysilane,
(3,4-epoxycyclohexyl)propyltrimethoxysilane,
3-acryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane,
3-aminopropylsilanetriol, 3-glycidoxypropyltriethoxysilane,
3-glycidoxypropyltrimethoxysilane,
3-methacryloxypropyltriethoxysilane,
3-methacryloxypropyltrimethoxysilane,
3-(triethoxysilyl)propylsuccinic acid silane,
aminoethylaminopropylmethyldiethoxysilane,
ammethylaminopropylmethyldimethoxysilane,
aminopropyltrialkoxysilane,
.beta.-(3,4-epoxycyclohexyl)ethyltriethoxysilane,
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,
.beta.-(3,4-epoxycyclohexyl)methyltriethoxysilane,
.beta.-(3,4-epoxycyclohexyl)methyltrimethoxysilane,
bis-1,2-(triethoxysilyl)ethane, bis-1,2-(trimethoxysilyl)ethane,
bis(triethoxysilylpropyl)amine, bis(trimethoxysilylpropyl)amine,
.gamma.-(3,4-epoxycyclohexyl)propyltriethoxysilane,
.gamma.-(3,4-epoxycyclohexyl)propyltrimethoxysilane,
.gamma.-acryloxypropyltriethoxysilane,
.gamma.-acryloxypropyltrimethoxysilane,
.gamma.-aminopropyltriethoxysilane,
.gamma.-aminopropyltrimethoxysilane,
.gamma.-methacryloxypropyltriethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane,
.gamma.-ureidopropyltrialkoxysilane,
N-2-aminoethyl-3-aminopropyltriethoxysilane,
N-2-aminoethyl-3-aminopropyltrimethoxysilane,
N-2-aminomethyl-3-aminopropyltriethoxysilane,
N-2-aminomethyl-3-aminopropyltrimethoxysilane,
N-(3-(trimethoxysilyl)propyl)ethylenediamine,
N-.beta.-(aminoethyl)-.gamma.-aminopropyltriethoxysilane,
N-.beta.-(aminoethyl)-.gamma.-aminopropyltrimethoxysilane,
N-(.gamma.-triethoxysilylpropyl)diethylenetriamine,
N-(.gamma.-trimethoxysilylpropyl)diethylenetriamine,
N-(.gamma.-triethoxysilylpropyl)dimethylenetriamine,
N-(.gamma.-trimethoxysilylpropyl)dimethylenetriamine,
poly(aminoalkyl)ethyldialkoxysilane,
poly(aminoalkyl)methyldialkoxysilane,
tris(3-(triethoxysilyl)propyl)isocyanurate,
tris(3-(trimethoxysilyl)propyl)isocyanurate,
ureidopropyltrialkoxysilane and vinyl triacetoxysilane.
In individual embodiment variants, the aqueous composition
optionally contains at least one
silane/silanol/siloxane/polysiloxane with a group containing
fluorine. The hydrophilicity/hydrophobicity may also be adjusted in
a targeted manner, depending on the choice of the silane
compound(s).
In many embodiments of the aqueous silane-based pretreatment
composition, preferably at least one
silane/silanol/siloxane/polysiloxane that is at least partially
hydrolyzed, and an at least partially condensed
silane/silanol/siloxane/polysiloxane is added to the aqueous
silane-based pretreatment composition. In combining the aqueous
composition in particular, at least one
silane/silanol/siloxane/polysiloxane is preferably added. Such an
additive is especially preferred.
In many embodiments at least one
silane/silanol/siloxane/polysiloxane, which is at least largely
and/or completely hydrolyzed and/or at least largely and/or
completely condensed, may be added to the aqueous silane-based
pretreatment composition. In many embodiment variants, a
nonhydrolyzed silane does not bind as well to the metallic surface
as does a silane/silanol that is at least partially hydrolyzed. A
largely hydrolyzed silane/silanol/siloxane that has been condensed
very little or not at all binds much better to the metallic surface
in many embodiment variants than an at least partially hydrolyzed
and largely condensed silane/silanol/siloxane/polysiloxane. A
completely hydrolyzed and largely condensed
silanol/siloxane/polysiloxane has only a low tendency to be bound
chemically to the metallic surface in many embodiment variants.
In many embodiments, the aqueous silane-based pretreatment
composition may contain at least one added silanol, which has
multiple branching and/or three to 12 amino groups per
molecule.
In many embodiments, at least one siloxane and/or polysiloxane
which contains little or no silanes/silanols, e.g., less than 20%
by weight or less than 40% by weight of the total of
silane/silanol/siloxane/polysiloxane may be added to the aqueous
silane-based pretreatment composition in addition and/or as an
alternative to silane(s)/silanol(s). The siloxane and/or
polysiloxane preferably has/have a short chain and is/are
preferably applied by a Roll Coater treatment. This then affects
the coating, optionally by greater hydrophobicity and higher
corrosion protection on bare metal.
The aqueous silane-based pretreatment composition preferably
contains at least two or even at least three compounds of titanium,
hafnium and zirconium. These compounds may differ in their cations
and/or in their anions. The aqueous composition, in particular the
bath composition, preferably contains at least one complex fluoride
b), especially preferably at least two complex fluorides selected
from complex fluorides of titanium, hafnium and zirconium. Their
difference preferably lies not only in the type of complex. The
aqueous silane-based pretreatment composition, in particular the
bath composition, preferably contains compounds b) selected from
compounds of titanium, hafnium and zirconium in the range of 0.01
to 50 g/L, calculated as the sum of the corresponding metals. This
content is especially preferably in the range of 0.05 to 30 g/L,
most especially preferably in the range of 0.08 to 15 g/L, in
particular in the range of 0.1 to 5 g/L.
The aqueous silane-based pretreatment composition preferably
contains at least one complex fluoride, where the complex fluoride
content is in particular in the range of 0.01 to 100 g/L,
calculated as the sum of the corresponding metal complex fluorides
as MeF.sub.6. The content is preferably in the range of 0.03 to 70
g/L, especially preferably in the range of 0.06 to 40 g/L, most
especially preferably in the range of 1 to 10 g/L. The complex
fluoride may in particular be in the form of MeF.sub.4 and/or
MeF.sub.6 but it also may be in other stages and/or intermediate
stages. In many embodiment variants, there is advantageously at
least one titanium complex fluoride and at least one zirconium
complex fluoride present at the same time. In many cases, it may be
advantageous to have at the same time at least one MeF.sub.4
complex and at least MeF.sub.6 complex in the composition, in
particular one TIF.sub.6 and one ZrF.sub.4 complex at the same
time. It may be advantageous here to adjust these complex fluoride
relationships already in the concentrate and to transfer them to
the bath in this way.
The individual complex fluorides surprisingly do not have a
negative influence on each other when combined but instead manifest
an unexpected positive enhancing effect. These additives based on
complex fluoride evidently act in a similar or identical manner. If
a combination of complex fluorides based on titanium and zirconium
is used instead of just one complex fluoride based on titanium or
one complex fluoride based on zirconium, this surprisingly always
yields significantly better results than those achieved with a
single one of these additives. On the surface, a complex fluoride
based on titanium and/or zirconium would presumably be out of the
question as an oxide and/or hydroxide.
It has surprisingly been found that a good multimetal treatment
with a single aqueous composition is possible only when using a
complex fluoride, and a very good multimetal treatment with a
single aqueous composition is possible only when at least two
different complex fluorides are used, for example, those based on
titanium and zirconium. The individual complex fluorides used in a
wide variety of experiments never yielded results that were equally
good for the combination of these two complex fluorides, regardless
of which additives were added in addition.
As an alternative or in addition to at least one complex fluoride,
a different type of compound of titanium, hafnium and zirconium may
also be added, for example, at least one hydroxycarbonate and/or at
least one other water-soluble or weakly water-soluble compound,
such as at least one nitrate and/or at least one carboxylate, for
example.
Preferably only species of cations and/or corresponding compounds
selected from the following group are used as the cations and/or
the corresponding compounds c): aluminum, barium, magnesium,
calcium, indium, yttrium, lanthanum, cerium, vanadium, niobium,
tantalum, molybdenum, tungsten, lead, manganese, iron, cobalt,
nickel, copper, silver, bismuth, tin and zinc, especially
preferably from the group of aluminum, magnesium, calcium, yttrium,
lanthanum, cerium, vanadium, molybdenum, tungsten, manganese, iron,
cobalt, copper, bismuth, tin and zinc, not to mention trace amounts
of less than 0.005 g/L in the bath composition, except for copper
and silver, calculated as metal. Most especially preferred as
cations and/or corresponding compounds c) are only species of
cations and/or corresponding compounds selected from the group of
magnesium, calcium, yttrium, lanthanum, cerium, manganese, iron,
cobalt, copper, tin and zinc are selected from the group of
calcium, yttrium, manganese, iron, cobalt, copper, tin and zinc,
apart from trace contents of less than 0.005 g/L each in the bath
composition, except for copper and silver, calculated as metal.
Individual ones of these cations and/or compounds may also be
preferred to increase the conductivity of the respective coating
and/or an interface, to improve the binding to a coating and/or to
use similar cations in the aqueous silane-based pretreatment
composition, in at least one water rinse and/or in
electrodeposition coating.
On the other hand, it has surprisingly been found that cations of
iron and zinc and therefore also the presence of corresponding
compounds in the bath, which may contribute to an increased extent
to the dissolving of such ions out of the metal surface, especially
with acidic compositions, do not have negative effects on the bath
performance, the formation of layers and the layer properties over
wide ranges of content.
The aqueous silane-based pretreatment composition, in particular
the bath composition, preferably has a cation content and/or a
content of corresponding compounds c) in the range of 0.01 to 20
g/L, calculated as the sum of the metals. It is especially
preferably in the range of 0.03 to 15 g/L, most especially
preferably in the range of 0.06 to 10 g/L, in particular in the
range of 0.1 to 6 g/L. The amount of each individual type of cation
and/or compounds c) in the aqueous silane-based pretreated
composition is most especially preferably in the range of 0.005 to
0.500 g/L, from 0.008 to 0.100 g/L or from 0.012 to 0.050 g/L,
calculated as metal, not including copper and silver cation
contents, which may have a definite influence even in smaller
amounts such as 0.001 to 0.030 g/L, where 1 ppm corresponds to
0.001 g/L. Depending on the type of cation and/or the corresponding
compound, the preferred contents in the aqueous silane-based
pretreatment composition are of a different order of magnitude.
The aqueous silane-based pretreatment composition preferably
contains at least one type of cation selected from cations of
cerium, chromium, iron, calcium, cobalt, copper, magnesium,
manganese, molybdenum, nickel, niobium, tantalum, yttrium, zinc,
tin and other lanthanides and/or at least one corresponding
compound. In many embodiments, at least two, at least three or at
least four different types of cations are added or at least three,
at least four or at least five different types of cations are found
in the aqueous silane-based pretreatment composition. Combinations
of cations and/or their compounds selected from group 1) of cations
of aluminum, iron, cobalt, copper, manganese, tin and zinc, 2) of
cations of cerium, iron, calcium, magnesium, manganese, yttrium,
zinc and tin, 3) of cations of copper, manganese and zinc or 4) of
cations of aluminum, iron, calcium, copper, magnesium, manganese
and zinc are especially preferred. Preferably not all the cations
contained in the aqueous composition are dissolved out of the
metallic surface, not only by the aqueous composition but also at
least partially or even largely added to the aqueous composition. A
freshly prepared bath may therefore be free of certain cations
and/or compounds, which are released and/or are formed only by
reactions with metallic materials and/or reactions in the bath.
The addition of manganese ions and/or at least one manganese
compound has surprisingly been found to be especially advantageous.
Although evidently no manganese compound or almost no manganese
compound is deposited on the metallic surface, this addition
evidently promotes the deposition of
silane/silanol/siloxane/polysiloxane and thus improves the
properties of the coatings significantly. Adding magnesium ions
and/or at least one magnesium compound has also been found to be
unexpectedly advantageous because this additive promotes the
deposition of titanium and/or zirconium compounds, presumably as
the oxide and/or hydroxide, on the metallic surface, and thus
greatly improves the properties of the coating. Combined addition
of magnesium and manganese leads in part to a further improvement
in the coatings. However, addition of copper ions in the range of
0.001 to 0.030 g/L has been found to have a significant influence.
Addition of indium and/or tin has also proven especially suitable.
At a higher calcium ion content, it is important to be sure that no
destabilization of a complex fluoride occurs due to the formation
of calcium fluoride.
The aqueous silane-based pretreatment composition preferably
contains at least one type of cation and/or corresponding compounds
selected from alkaline earth metal compounds in the range of 0.01
to 50 g/L, calculated as the corresponding compounds, especially
preferably in the range of 0.03 to 35 g/L, most especially
preferably in the range of 0.06 to 20 g/L, in particular in the
range of 0.1 to 8 g/L or up to 1.5 g/L. The alkaline earth metal
ions and/or corresponding compounds may help to potentiate the
deposition of compounds based on titanium and/or zirconium, which
is often advantageous in particular for increasing the corrosion
resistance.
The aqueous silane-based pretreatment composition preferably
contains an amount of at least one type of cation selected from
cations of aluminum, iron, cobalt, magnesium, manganese, nickel,
yttrium, tin, zinc and lanthanides and/or at least one
corresponding compound c), in particular in the range of 0.01 to 20
g/L, calculated as the sum of the metals. It is especially
preferably in the range of 0.03 to 15 g/L, most especially
preferably in the range of 0.06 to 10 g/L, in particular in the
range of 0.020 to 6 g/L, 0.040 to 1.5 g/L, 0.060 to 0.700 g/L or
0.080 to 0.400 g/L.
The composition preferably contains at least one organic compound
d) selected from monomers, oligomers, polymers, copolymers and
block copolymers, in particular at least one compound based on
acryl, epoxide and/or urethane. In addition or alternatively, at
least one organic compound with at least one silyl group may also
be used. In many embodiments, it is preferable to use such organic
compounds with a content or even a higher content of OH groups,
amine groups, carboxylate groups, isocyanate groups and/or
isocyanurate groups.
The aqueous silane-based pretreatment composition preferably
contains at least one organic compound d) selected from monomers,
oligomers, polymers, copolymers and block copolymers in the range
of 0.01 to 200 g/L, calculated as the solid additive. The content
is especially preferably in the range of 0.03 to 120 g/L, most
especially preferably in the range of 0.06 to 60 g/L, in particular
in the range of 0.1 to 20 g/L. In many embodiment variants, such
organic compounds may help to make the formation of the coating
more uniform. This compounds may contribute to the development of a
more compact, denser, chemically more resistant and/or more
water-resistant coating in comparison with coatings based on
silane/silanol/siloxane/polysiloxane, etc. without these compounds.
Depending on the choice of organic compound(s), the
hydrophilicity/hydrophobicity may also be adjusted in a targeted
manner. However, a strongly hydrophobic coating is problematical in
many applications because of the required binding of water-based
paints in particular. When using an additive of at least one
organic compounds, a combination with compounds with a certain
functionality has proven to be especially advantageous such as, for
example, compounds based on
amines/diamines/polyamines/urea/imines/diimines/polyimines and/or
their derivatives, compounds based on capped isocyanates,
isocyanurates and/or melamine compounds, in particular, compounds
with carboxyl groups and/or hydroxyl groups, such as carboxylates,
long-chain sugar-type compounds, e.g., (synthetic) starch,
cellulose, saccharides, long-chain alcohols and/or their
derivatives. Of the long-chain alcohols, in particular those with 4
to 20 carbon atoms are added such as a butanediol, a butyl glycol,
a butyl diglycol, an ethylene glycol ether such as ethylene glycol
monobutyl ether, ethylene glycol monoethyl ether, ethylene glycol
monomethyl ether, ethyl glycol propyl ether, ethylene glycol hexyl
ether, diethylene glycol methyl ether, diethylene glycol ethyl
ether, diethylene glycol butyl ether, diethylene glycol hexyl ether
or a propylene glycol ether such as propylene glycol monomethyl
ether, dipropylene glycol monomethyl ether, tripropylene glycol
monomethyl ether, propylene glycol monobutyl ether, dipropylene
glycol monobutyl ether, tripropylene glycol monobutyl ether,
propylene glycol monopropyl ether, dipropylene glycol monopropyl
ether, tripropylene glycol monopropyl ether, propylene glycol
phenyl ether, trimethyl pentanediol diisobutyrate, a
polytetrahydrofuran, a polyether polyol and/or a polyester
polyol.
The weight-based ratio of compounds based on
silane/silanol/siloxane/polysiloxane is calculated, based on the
corresponding silanols, to compounds based on organic polymers,
calculated as a solid additive in the composition, is preferably in
the range of 1:0.05 to 1:30, especially preferably in the range of
1:0.1 to 1:2, most especially preferably in the range of 1:0.2 to
1:20. In many embodiment variants, this ratio is in the range of
1:0.25 to 1:12, in the range of 1:0.3 to 1:8 or in the range of
1:0.35 to 1:5.
It has surprisingly been found that addition of organic polymer
and/or copolymer in particular greatly improves the corrosion
resistance on iron and steel and is especially advantageous for a
greater process reliability and consistently good coating
properties.
The aqueous silane-based pretreatment composition optionally
contains an amount of silicon-free compounds with at least one
amino group, urea group and/or ureido group, in particular
compounds of amine/diamine/polyamine/urea/imine/diimine/polyimine
and derivatives therefore, preferably in the range of 0.01 to 30
g/L, calculated as the sum of the corresponding compounds. The
amount is especially preferably in the range of 0.03 to 22 g/L,
most especially preferably in the range of 0.06 to 15 g/L, in
particular in the range of 0.1 to 10 g/L. Preferably at least one
compound, e.g., aminoguanidine, monoethanolamine, triethanolamine
and/or a branched urea derivative with an alkyl radical is added.
An additive to aminoguanidine in particular substantially improves
the properties of the coatings according to the invention.
The aqueous silane-based pretreatment composition optionally
contains an amount of anions of nitrite and compounds with a nitro
group, preferably in the range of 0.01 to 10 g/L, calculated as the
sum of the corresponding compounds. The amount is especially
preferably in the range of 0.02 to 7.5 g/L, most especially
preferably in the range of 0.03 to 5 g/L, in particular in the
range of 0.05 to 1 g/L. This substance is preferably added as
nitrous acid HNO.sub.2, as an alkali nitrite, as ammonium nitrite,
as nitroguanidine and/or as paranitrotoluene sulfonic acid, in
particular as sodium nitrite and/or nitroguanidine.
It has surprisingly been found that addition of nitroguanidine in
particular to the aqueous silane-based pretreatment composition
perceptibly improves the appearance of the coatings according to
the invention, making them appear to be very uniform, and
perceptibly increases the quality of the coating. This has a very
positive effect in particular on "sensitive" metallic surfaces,
such as sandblasted iron and/or steel surfaces. Addition of
nitroguanidine significantly improves the properties of the
coatings according to the invention.
It has surprisingly been found that addition of nitrite can
significantly reduce the tendency of iron and steel surfaces in
particular to rust.
The aqueous silane-based pretreatment composition optionally
contains compounds based on peroxide, for example, hydrogen
peroxide and/or at least one organic peroxide, preferably in the
range of 0.005 to 5 g/L, calculated as H.sub.2O.sub.2. The amount
is especially preferably in the range of 0.006 to 3 g/L, most
especially preferably in the range of 0.008 to 2 g/L, in particular
in the range of 0.01 to 1 g/L. In the presence of titanium, a
titanium-peroxo complex, which turns the solution and/or dispersion
orange is often formed in the bath. However, this color is
typically not present in the coating because this complex is
evidently not incorporated into the coating as such. The titanium
content and/or peroxide content can therefore be estimated on the
basis of the color of the bath. The substance is preferably added
as hydrogen peroxide.
It has unexpectedly been found that addition of hydrogen peroxide
to the aqueous silane-based pretreatment composition according to
the invention improves the optical quality of the coated
substrates.
The aqueous silane-based pretreatment composition optionally
contains an amount of phosphorus-containing compounds preferably in
the range of 0.01 to 20 g/L, calculated as the sum of the
phosphorus-containing compounds. These compounds preferably contain
phosphorus and oxygen, in particular as oxy anions and as the
corresponding compounds. The content is especially preferably in
the range of 0.05 to 18 g/L, most especially preferably in the
range of 0.1 to 15 g/L, in particular in the range of 0.2 to 12
g/L. Preferably at least one orthophosphate, an oligomer and/or
polymer phosphate and/or a phosphonate is added as substance
d.sub.4). The at least one orthophosphate and/or salts thereof
and/or esters thereof may be, for example, at least one alkali
phosphate, iron, manganese and/or zinc-containing orthophosphate
and/or at least one of their salts and/or esters. Instead of or in
addition to this, at least one metaphosphate, polyphosphate,
pyrophosphate, triphosphate and/or salts thereof and/or esters
thereof may be added. For example, at least one phosphonic acid,
e.g., at least one alkyl diphosphonic acid and/or salts thereof
and/or esters thereof may be added as the phosphonate. The
phosphorus-containing compounds of this substance are not
surfactants.
It has surprisingly been found that addition of orthophosphate to
the aqueous silane-based pretreatment composition according to the
invention greatly improves the quality of the coatings in
particular on electrolytically galvanized substrates.
it has also surprisingly been found that addition of phosphonate to
the aqueous silane-based pretreatment composition according to the
invention significantly improves the corrosion resistance of
aluminum-rich surfaces, especially in the CASS test values.
The aqueous silane-based pretreatment composition optionally
contains at least one type of anions selected from carboxylates
such as acetate, butyrate, citrate, formate, fumarate, glycolate,
hydroxyacetate, lactate, laurate, maleate, malonate, oxalate,
propionate, stearate, tartrate and/or at least one corresponding
compound that is only partially dissociated or not at all.
The aqueous silane-based pretreatment composition optionally
contains carboxylate anions and/or carboxylate compounds in the
range of 0.01 to 30 g/L, calculated as the sum of the corresponding
compounds. The content is especially preferably in the range of
0.05 to 15 g/L, most especially preferably in the range of 0.1 to 8
g/L, in particular in the range of 0.3 to 3 g/L. Especially
preferably at least one citrate, lactate, oxalate and/or tartrate
may be added as the carboxylate. The addition of at least one
carboxylate may help to complex a cation and keep it in solution
more easily, so that a higher bath stability and controllability of
the bath can be achieved. It has surprisingly been found that
binding of silane to the metallic surface can be facilitated and
improved to some extent by a carboxylate content.
The aqueous silane-based pretreatment composition preferably also
contains an amount of nitrate. It preferably contains nitrate in an
amount in the range of 0.01 to 20 g/L, calculated as the sum of the
corresponding compounds. The content is especially preferably in
the range of 0.03 to 12 g/L, most especially preferably in the
range of 0.06 to 8 g/L, in particular in the range of 0.1 to 5 g/L.
Nitrate may help to make the coating formation more uniform on
steel in particular. Nitrite may in some circumstances be converted
to nitrate, but usually only partially. Nitrate may be added in
particular as an alkali metal nitrate, ammonium nitrate, heavy
metal nitrate, as nitric acid and/or corresponding organic
compounds. The nitrate may significantly reduce the tendency to
rust, in particular on steel and iron surfaces. The nitrate may
optionally contribute toward the development of a defect-free
coating and/or an extremely even coating, which may possibly be
free of optically recognizable marks.
The aqueous silane-based pretreatment composition preferably
contains an amount of at least one type of cation selected from
alkali metal ions, ammonium ions and corresponding compounds in
particular potassium and/or sodium ions and/or at least one
corresponding compound.
The aqueous silane-based pretreatment composition optionally
contains an amount of free fluoride in the range of 0.001 to 3 g/L,
calculated as F.sup.-. The amount is preferably in the range of
0.01 to 1 g/L, especially preferably in the range of 0.02 to 0.5
g/L, most especially preferably in the range of 0.1 g/L. It has
been found that in many embodiment variants it is advantageous to
have a low free fluoride content in the bath because then the bath
can be stabilized in many embodiments. If the free fluoride content
is too high, sometimes that may have a negative influence on the
cation deposition rate. In addition, non-dissociated fluoride
and/or fluoride not bound in a complex may also occur in the range
of 0.001 to 0.3 g/L in many cases. Such an additive is preferably
added in the form of hydrofluoric acid and/or the salts
thereof.
The aqueous silane-based pretreatment composition preferably
contains an amount of at least one fluoride-containing compound
and/or fluoride anions, calculated as F.sup.-, and without taking
into account complex fluorides, in particular at least one fluoride
of alkali fluoride(s), ammonium fluoride and/or hydrofluoric acid,
especially preferably in the range of 0.001 to 12 g/L, most
especially preferably in the range of 0.005 to 8 g/L, in particular
in the range of 0.01 to 3 g/L. The fluoride ions and/or the
corresponding compounds may help to control the deposition of the
metal ions on the metallic surface, so that, for example, the
deposition of the at least one zirconium compound may be increased
or reduced as needed. The weight ratio of the sum of the complex
fluorides, calculated as the sum of the respective metals, to the
sum of the free fluorides, calculated as F.sup.- is preferably
greater than 1:1, especially preferably greater than 3:1, most
especially preferably greater than 5:1, especially preferably
greater than 10:1.
With the method according to the invention, the aqueous
silane-based pretreatment composition may contain at least one
compound selected from alkoxides, carbonates, chelates, surfactants
and additives, for example, biocides and/or foam suppressants.
Acetic acid, for example, may be added as a catalyst for hydrolysis
of a silane. The pH of the bath may be blunted, i.e., for example,
with ammonia/ammonium hydroxide, an alkali hydroxide and/or a
compound based on an amine, such as monoethanolamine, for example,
whereas the pH of the bath is preferably lowered using acetic acid,
hydroxyacetic acid and/or nitric acid. These substances can
influence the pH.
The amounts and/or additives listed above usually have a promoting
effect in the aqueous silane-based pretreatment compositions
according to the invention in that they help to further improve the
good properties of the aqueous basic composition of components a),
b) and solvent(s) according to the invention. These additives are
usually used in the same way if only one titanium compound or only
one zirconium compound or a combination of these is used. However,
it has surprisingly been found that the combination of at least one
titanium compound and at least one zirconium compound in particular
as complex fluorides can significantly improve the properties of
the coatings produced with them in particular. The various
additives surprisingly act as in a modular system and make a
significant contribution toward optimization of the respective
coating. Especially when using a so-called multimetal mix, such as
that often encountered in the pretreatment of vehicle bodies and in
the treatment or pretreatment of various small parts of assembly
parts, the aqueous silane-based pretreatment composition has proven
very successful because it can be optimized with various additives
specifically for the respective multimetal mix and its particulars
and requirements.
In the method according to the invention, a mix of various metallic
materials can be coated with the aqueous silane-based pretreatment
composition, for example, in the case of vehicle bodies or various
small parts. For example, substrates with metallic surfaces can be
selected here from cast iron, steel, aluminum, aluminum alloys,
magnesium alloys, zinc and zinc alloys in any mix can be coated
simultaneously and/or in succession according to the invention,
wherein the substrates may at least partially be coated
metallically and/or at least partially may consist of at least one
metallic material.
Inasmuch as at least one additional component and/or traces of
additional substances are not present, the remainder to a total of
1000 g/L consists of water or water and at least one organic
solvent such as ethanol, methanol, isopropanol and/or
dimethylformamide (DMF). The organic solvent content in most
embodiments is particularly low or even zero. Because of the
hydrolysis of at least one silane that is present, at least one
alcohol may be present in particular, for example, ethanol and/or
methanol. In particular, preferably no organic solvent is
added.
The aqueous silane-based pretreatment composition is preferably or
essentially free of all types of particles or particles having an
average diameter larger than 0.2 .mu.m that may optionally be
added, for example, based on oxides, e.g., SiO.sub.2. Many
compositions are also free of additives of organic monomers,
oligomers, polymers, copolymers and/or block copolymers.
Only if the coatings produced with the aqueous silane-based
pretreatment composition have been dried to a greater extent, for
example, for 5 minutes at 80.degree. C. PMT (peak metal
temperature), for example, 25 minutes at 70.degree. C. PMT or more,
these coatings are usually insensitive to water because
condensation of the silanes, silanols, siloxanes, polysiloxanes has
advanced to a greater extent. The degree of drying, which is
associated with condensation and leads to a rinse-fastness of the
coating containing siloxane and/or polysiloxane, varies according
to the phase, the coating and the type of rinse.
The applied siloxane/polysiloxane-containing coating is preferably
applied freshly and/or is optionally not dried at all or is dried
only slightly when rinsed. The coating is preferably rinsed within
20 seconds after being applied. Since the silane-containing aqueous
composition preferably has a temperature in the range of 10 to
50.degree. C. when applied, especially preferably in the range of
15 to 35.degree. C., and since the object to be coated preferably
has a temperature in the range of 10 to 50.degree. C., especially
preferably in the range of 15 to 35.degree. C., these temperatures
are usually not so high and are usually not so different that the
wet film will dry rapidly.
The aqueous silane-based pretreatment composition preferably
contains a small amount of or is free of or essentially free of
larger amounts of the substances that cause water hardness, such as
calcium, in amounts in excess of 1 g/L. The composition is
preferably free or almost free of lead, cadmium, chromate, cobalt,
nickel and/or other toxic heavy metals. Such substances are
preferably not added intentionally, but at least one heavy metal
may be dissolved out of a metallic surface, for example, it may be
entrained from another bath and/or may occur as an impurity. The
composition preferably contains a small amount of or is essentially
or entirely free of bromide, chloride and iodide because these may
contribute toward corrosion under some circumstances.
The layer thickness of the coatings produced with the aqueous
silane-based pretreatment composition is preferably in the range of
0.005 to 0.3 .mu.m, especially preferably in the range of 0.01 to
0.25 .mu.m, most especially preferably in the range of 0.02 to 0.2
.mu.m, often at approx. 0.04 .mu.m, at approx. 0.06 .mu.m, at
approx. 0.08 .mu.m, at approx. 0.1 .mu.m, at approx. 0.12 .mu.m, at
approx. 0.14 .mu.m, at approx. 0.16 .mu.m or at approx. 0.18 .mu.m.
The coatings containing organic monomer, oligomer, polymer,
copolymer and/or block copolymer are often somewhat thicker than
those that are free or almost free thereof.
Preferably a coating with a layer weight in the range of 1 to 200
mg/m.sup.2, based on the titanium and/or zirconium content, is
preferably formed with the aqueous silane-based pretreatment
composition. This layer weight is especially preferably in the
range of 5 to 150 mg/m.sup.2, most especially in the range of 8 to
120 mg/m.sup.2, in particular approx. 10, approx. 20, approx. 30,
approx. 40, approx. 50, approx. 60, approx. 70, approx. 80, approx.
90, approx. 100 or approx. 110 mg/m.sup.2.
A coating with a layer weight in the range of 0.2 to 1000
mg/m.sup.2, based only on siloxane/polysiloxane and calculated as
the corresponding largely thoroughly condensed polysiloxane is
preferably formed with the aqueous silane-based pretreatment
composition. This layer weight is especially preferably in the
range of 2 to 200 mg/m.sup.2, most especially preferably in the
range of 5 to 150 mg/m.sup.2, in particular approx. 10, approx. 20,
approx. 30, approx. 40, approx. 50, approx. 60, approx. 70, approx.
80, approx. 90, approx. 100, approx. 110, approx. 120, approx. 130
or approx. 140 mg/m.sup.2.
It has surprisingly been found that the quality of the silane-based
pretreatment coating and the composition of the water for rinsing
after the silane pretreatment have a significant effect on the
quality of the electrodeposition coating applied subsequently and
to some extent even affect the layers of paint which follow.
In rinsing, preferably a liquid, particle-free fluid, in particular
water or a solution is used as the fluid. The fluid is especially
preferably water of city tap water quality, a pure water quality
such as deionized water or a water quality containing at least one
surfactant, for example. A surfactant can contribute toward a
greater evenness of the wet film. The surfactant can be added to
the water, which may also be an aqueous rinse solution, as a
surfactant mixture, wherein preferably an aqueous solution
containing at least one surfactant and optionally also containing
at least one additive, e.g., at least one solubilizer, at least one
surface-active substance such as a phosphonate, at least one
substance which influences the electrodeposition coating and/or the
electrodeposition paint may be used. Evidently basically any
surfactant may be added as the surfactant, but nonionic surfactants
in particular, such as fatty alcohol glycol ethers, are preferred.
It is advantageous to select low-foaming surfactants or those that
cause little or almost no foaming and/or surfactant-containing
mixtures for applications which may easily result in foam
production as in after-rinsing by spraying. These mixtures may
additionally contain a foam suppressant, for example, and/or a
solubilizer and may have a low, very low or almost no tendency to
foaming, either individually or in combination in spray processes,
for example. The at least one surfactant here may fundamentally be
selected from the group of anionic, cationic, nonionic, amphoteric
and other surfactants, for example, low-foam block copolymers. It
may be advantageous, for example, to use a combination of at least
two surfactants or at least three surfactants. A combination of
surfactants from different surfactant classes may be selected here,
for example, one or two nonionic surfactants together with a
cationic surfactant. Especially preferably at least two chemically
different surfactants are selected from the nonionic surfactants.
On the one hand, a combination of at least one surfactant per class
selected from the classes of anionic, cationic, nonionic,
amphoteric and other surfactants is especially preferred, in
particular a combination of at least one nonionic surfactant with
at least one surfactant from another surfactant class. On the other
hand, it is also possible to use only nonionic surfactants in
combination. The nonionic surfactants are advantageously selected
from linear ethoxylates and/or propoxylates and preferably those
with alkyl groups of 8 to 18 carbon atoms. If surfactants with a
turbidity point are used, i.e., surfactants of a nonionic type, it
is advantageous that these surfactants are no longer present in
dissolved form in the washing medium of the washing process above
the turbidity point in order to minimize the foaming, in particular
when spraying. A mixture of an ethoxylated alkylamine together with
at least one ethoxylated or ethoxylated and propoxylated alkyl
alcohol may be especially advantageous for adjusting a low-foaming
tendency. In particular with a combination of surfactants, the
wetting and foam-suppressant properties, such as beading of the
rinse water and the low-foaming property can be optimized at the
same time, but the properties of the electrodeposition coating such
as the visual impression of the electrodeposition coating, for
example, unevenness and streaks, uniformity of the layer
thicknesses of the electrodeposition coating, improvement in the
throwing power of the paint in electrodeposition coating, in
particular on undercut locations of the substrate to be coated as
well as preventing marks can be influenced surprisingly
advantageously with a combination of surfactants at the same time.
On the other hand, addition of at least one solubilizer, for
example, cumene sulfonate or a glycol, in particular dipropylene
glycol, a polyglycol, a polyacrylamide and/or a modified
polyacrylamide, a biocide, a fungicide and/or an agent to adjust
the pH, for example, an amine or an organic and/or inorganic acid
may also be used in the rinse water. Therefore, in a preferred
method, an additive to the rinse water is used when rinsing the
silane-based pretreatment coating, such that the wetting and foam
suppressant properties are improved at the same time through the
combination of at least two different surfactants and optionally
additional additives such as solubilizers. In the method according
to the invention, an additive with a surfactant content is used in
the rinse water, thereby having an advantageous influence on the
properties of the electrodeposition paint and the electrodeposition
coating. The electrodeposition coated substrates, whose aqueous
silane-based pretreatment coating has been rinsed with water
containing a surfactant, also displayed a significantly improved
paint throwing power in comparison with electrodeposition coated
substrates rinsed with water that did not contain a surfactant.
The surfactant content in the rinse water for the after-rinse
following the silane-based pretreatment is preferably in the range
of 0.001 to 1.6 g/L, especially preferably in the range of 0.01 to
1.0 g/L or 0.05 to 0.6 g/L.
The fluid (=water for rinsing) preferably has a temperature in the
range of 10.degree. C. to 50.degree. C., especially preferably in
the range of 15.degree. C. to 35.degree. C. The objects coated with
the wet film may be wetted by dipping into a bath and into a liquid
spray or film, by spraying, splashing or some similar form of
wetting in the liquid film and/or jet of a rinsing ring. The liquid
jet or film preferably does not strike the coating containing the
silane/silanol/siloxane/polysiloxane at a pressure of more than 2
bar.
As an alternative to the process sequence proposed so far, which is
also based on the process sequence of the following Table 1, it is
possible, on the one hand, to perform a prerinse and/or a first
silane coating with an aqueous composition before the silane-based
pretreatment according to the invention, such that this composition
contains at least one silane, at least one compound selected from
fluoride-free compounds of titanium, hafnium, zirconium, aluminum
and boron, at least one highly dilute alkaline solution, such as
NaOH and/or at least one complex fluoride and/or, on the other
hand, to perform a rinsing after the aqueous silane pretreatment
with an aqueous composition that contains not only water and
optionally at least one surfactant for making the wet film more
uniform.
Basically any type of electrodeposition coating may be used as the
electrodeposition paint in the method according to the invention.
In individual embodiment variants, it may be advantageous to adjust
the composition of the aqueous silane-based pretreatment and/or the
composition of the water for rinsing after this pretreatment to the
type of electrodeposition paint that is used, in particular with
respect to the surfactant(s) used, which do not have an interfering
effect on the electrodeposition paint and/or the electrodeposition
coating.
The coatings produced using the aqueous silane-based pretreatment
composition according to the invention and then with an
electrodeposition paint may then also be coated as needed with at
least one primer, lacquer, adhesive and/or lacquer-type organic
composition, wherein optionally at least one of the additional
coatings is cured by heating and/or irradiation.
Alternatively or in addition to the procedure with the aqueous
rinse containing surfactant after the pretreatment with the
silane-based composition, an aqueous treatment with an amount of at
least one iron compound dissolved in water may be performed before
the pretreatment with the silane-based composition. This
composition is preferably alkaline, in particular in a pH range
from 9 to 14. This composition may be an alkaline cleaning agent,
for example, which is used in at least one process step and
contains an amount of at least one iron compound in at least one
process step. In another embodiment, however, this composition may
also be free of many or all additives of a typical cleaning agent
and may serve as an aqueous iron-containing rinse, for example,
which may then be used before, during and/or after the cleaning
steps. This composition may fundamentally be at a temperature of
>0.degree. C. and <100.degree. C. at the time of its
application to metallic surfaces; in particular as a cleaning agent
composition, it may be at a temperature in the range of 32.degree.
C. to 78.degree. C. and especially preferably in the range of
38.degree. C. to 70.degree. C. or in the range of 40.degree. C. to
60.degree. C. when applied to metallic surfaces. The at least one
iron compound is preferably at least one Fe.sup.2+ compound
dissolved in water and/or at least one Fe.sup.3+ dissolved in
water. The total Fe content of the aqueous composition dissolved in
water and the total Fe content of the aqueous composition are
preferably in a range of 0.005 to 1 g/L. The amounts of Fe.sup.2+
compound dissolved in water are especially preferably in the range
of 0 to 0.5 g/L, and the amounts of Fe.sup.3+ compound dissolved in
water are preferably in the range of 0.003 to 0.5 g/L. The Fe
compounds dissolved in water may be added in particular in the form
of water-soluble salts such as, for example, sulfates and nitrates.
The coating is preferably rinsed at least once with water after
being cleaned, in particular at least once with tap water and at
least once with deionized water.
The metallic substrates coated by the method according to the
invention may be used in the automotive industry, for rail
vehicles, in the aviation and space industries, in equipment
design, in mechanical engineering, in the construction industry, in
the furniture industry, for the production of crash barriers,
lamps, profiles, linings or small parts, for the production of
vehicle bodies or vehicle body parts, individual components,
preassembled and/or connected elements preferably in the automotive
or aviation industries, for the production of appliances or systems
in particular household appliances, control systems, testing
equipment or construction elements.
The existing installations for cleaning and phosphating vehicle
bodies before painting often have the following process steps as
listed in the middle column of Table 1. The right-hand column lists
the process steps which have surprisingly been recommended for
cleaning and silane coating of vehicle bodies in a shortened
process sequence.
TABLE-US-00001 TABLE 1 Typical sequence of process steps in
phosphating and/or recommended sequence in silane coating of the
vehicle bodies Phosphating Silane coating Alkaline cleaning 1
heated heated Alkaline cleaning 2 heated heated Rinse 1 tap water
tap water Rinse 2 tap water deionized water Activating very often,
with Ti or Zn (omitted) phosphate Rinse 3 optionally unless
activated in (omitted) advance Pretreatment phosphating, heated
silane coating Rinse 4 tap water deionized water Rinse 5 deionized
water deionized water After-rinse solution optional (omitted) Rinse
6 deionized water (omitted) Rinse ring optional (omitted)
It has also surprisingly been found that it is not only possible to
produce coatings with certain solutions that are based not only on
silane, such that these coatings are not only adequately rinse-fast
to water, even without great drying of the freshly prepared
coating, but also have somewhat better layer properties than the
comparable coatings that have been dried thoroughly. Evidently the
silane-based coatings which have not been dried to a greater extent
are more reactive than a paint or paint-type of composition, such
as cathodic deposition paint, for example, to be more reactive and
to thereby have adequate adhesion. It is therefore possible to omit
the drying step, which has previously been considered essential,
and also to omit the drying channel, which was more than 10 meters
long in some cases.
Based on the trend in zinc-manganese-nickel phosphating of vehicle
bodies, which has been under development for several decades, the
current phosphate layers produced today are of an extremely high
quality. Nevertheless contrary to expectation it has been possible
to achieve the same high-quality coatings with the silane-based
coatings. With the method according to the invention, it is
surprisingly possible to perform the pretreatment of vehicle bodies
using solutions based on silane with relatively small amounts of
the aqueous compositions without any negative effect on the quality
of the coatings. However, if definitely larger amounts of the
components of the bath are selected, this raises costs, while the
quality of the coatings produced with such a composition usually
cannot be increased further.
With the method according to the invention, it is possible to
reduce the pretreatment step from 3 to 5 minutes for phosphating to
approx. 2 minutes for coating with silane-based coatings and to
omit the heating to temperatures often in the range of 50 to
60.degree. C. in the case of phosphating. However, if the
temperature of the composition is lower, the bath temperature is
preferably raised to temperatures in the range of 15 to 25.degree.
C.
With the method according to the invention, it is possible to
perform the pretreatment of vehicle bodies not only in shorter
installations but also in installations that can be operated much
less expensively while also being substantially more
environmentally acceptable because the amounts of sludge containing
heavy metals that must be disposed of can be reduced to a minimum
and because water can be circulated to a greater extent and because
the water throughput can be greatly reduced. Therefore the
consumption of chemicals as well as the expenditures in workup can
be greatly reduced because less than 1% of the sludge quantity that
has occurred in phosphating in the past, based on the metallic
surface to be coated is obtained, so that the cost of disposal of
chemical waste is greatly reduced.
Addition of manganese to the aqueous silane-based pretreatment
composition has surprisingly proven to be especially advantageous.
Although evidently little or no manganese compound is deposited on
the metallic surface, this addition greatly promotes the deposition
of silane/silanol/siloxane/polysiloxane on the metallic surface.
When nitroguanidine was added, it was surprisingly found that the
appearance of the coated plates was very uniform, in particular
even on sensitive surfaces such as sandblasted iron and/or steel
surfaces. Addition of nitrite unexpectedly resulted in a definite
reduction in the tendency of steel substrates to rust. It has
surprisingly been found that any addition which has a significant
positive effect as defined in this patent application also has an
additive effect in improving the coating according to the
invention. By selecting several additives as in a modular system,
the various properties of a multimetal system in particular can be
further optimized.
It has surprisingly been found that a good multimetal treatment
with a single aqueous composition is possible only if using a
complex fluoride, and a very good multimetal treatment with a
single aqueous silane-based pretreatment composition is possible
only if at least two different complex fluorides are used such as
those based on titanium and zirconium, for example. In a variety of
experiments, the individual complex fluorides that were used never
yielded results that were as good as those obtained with the
combination of these two complex fluorides, regardless of which
additives were additionally added.
It could not have been foreseen that such a great increase in the
quality of aqueous silane-based pretreatment compositions is
possible with the addition of silane/silanol/siloxane/polysiloxane
additive. However, a definite increase in the quality level was
surprisingly found in all experiments starting with aqueous
compositions based on a silane and just one complex fluoride based
on titanium or zirconium.
In addition, it was surprising that testing the paint adhesion,
even on steel, yielded rock fall test grades of one or two when a
composition containing at least one silane and at least one complex
fluoride was applied by the method according to the invention.
Steel was found to be the most problematical material for aqueous
compositions based on a silane and just one complex fluoride based
on titanium or zirconium, in particular with regard to corrosion
resistance (see B5, for example).
Experience has shown that the CASS test is problematical with
aluminum and aluminum alloys, but the results were much better than
expected with the compositions according to the present
invention.
EXAMPLES AND COMPARATIVE EXAMPLES
The examples (E) and the comparative examples (CE) according to the
invention as described below are presented to illustrate the
subject matter of the invention in greater detail.
According to Table 2, the aqueous bath compositions are prepared as
mixtures using prehydrolyzed silanes. They each contain a silane
and optionally also a small amount of at least one similar
additional silane, and here again, for the sake of simplicity, when
silane is mentioned, it is also understood to mean silane, silanol,
siloxane and/or polysiloxane, and as a rule, this variety of
compounds, to some extent similar compounds in even larger numbers,
is also run through in the development of the coating, so that
several similar compounds are frequently also present in the
coating. The prehydrolysis may also last for several days at room
temperature with vigorous stirring, depending on the silane, unless
the silanes to be used are already present in prehydrolyzed form.
To prehydrolyze the silane, the silane is added to water in excess
and optionally catalyzed with acetic acid. Acetic acid was added in
only a few individual embodiment variants merely to adjust the pH.
In some embodiment variants, acetic acid is already present as the
catalyst for hydrolysis. Ethanol is not added but it is formed by
hydrolysis. The finished mixture is used as a freshly prepared
mixture.
Then for each test, at least three sheets of cold-rolled steel
(CRS) are cleaned on both sides with an aqueous alkaline cleaning
agent and rinsed with process water and then afterwards with
deionized water as well as sheets of aluminum alloy Al6O16 and/or
hot-dip galvanized or electrolytically galvanized steel and/or
Galvanneal.RTM. (ZnFe layer on steel) are brought in contact with
the corresponding treatment fluid on both sides at 25.degree. C. by
spraying, dipping or Roll Coater treatment. Immediately thereafter,
the sheets pretreated in this way are rinsed briefly with deionized
water. The sheets from the comparative examples are then dried at
90.degree. C. PMT and next painted by a cathodic automotive dip
coating (CDC). However, after the aqueous silane-based
pretreatment, the sheet metal in the examples according to the
invention is rinsed and then immersed in the CDC bath immediately
after rinsing. Next the sheets are provided with a complete
commercial automotive paint coating (electro-dip coating, filler,
top coat or clear coat; total thickness of the layer package
including CDC approx. 105 .mu.m) and tested for their corrosion
resistance and paint adhesion. The compositions and properties of
the treatment baths as well as the properties of the coatings are
summarized in Table 2.
The organofunctional silane A is an amino-functional
trialkoxysilane and has one amino group per molecule. Like all the
silanes used here, it is present in the aqueous solution mostly or
completely in hydrolyzed form. The organofunctional silane B has a
terminal amino group and has one ureido group per molecule. The
nonfunctional silane C is a bis-trialkoxysilane. The corresponding
hydrolyzed molecule has up to 6 OH groups on two silicon atoms.
The complex fluorides of titanium and/or zirconium are used largely
on the basis of an MeF.sub.x complex, for example, MeF.sub.6
complex. Manganese and optionally small amounts of at least one
additional cation that is not mentioned in the table are added as
metallic manganese to the respective complex fluoride solution and
dissolved therein. This solution is added to the aqueous
composition. If no complex fluoride is used, then manganese nitrate
is added. The silylated epoxy polymer contains a small amount of
OH.sup.- and isocyanate groups and therefore 33333 can be
crosslinked chemically even subsequently at temperatures above
100.degree. C.
The silanes contained in the aqueous composition--concentrate
and/or bath--are monomers, oligomers, polymers, copolymers and/or
reaction products with additional components based on hydrolysis
reactions, condensation reactions and/or additional reactions. The
reactions take place mainly in solution, during drying and/or
optionally during curing of the coating, in particular at
temperatures above 70.degree. C. All concentrates and baths have
proven to be stable over a period of a week and do not undergo any
changes or develop any precipitates. No ethanol was added. Any
ethanol content in the compositions originates only from chemical
reactions.
In most examples and comparative examples, the pH is adjusted,
specific with ammonia in the presence of at least one complex
fluoride or in other cases with an acid. All baths have a good
quality of the solution and almost always good bah stability. There
are no precipitates in the baths. After coating with the
silane-containing solution, a brief rinsing is first performed once
with deionized water in the examples according to the invention and
in the comparative examples, immediately following the aqueous
silane-based pretreatment. The freshly applied wet film could not
be dried further because the samples were rinsed within 5 seconds
after applying the silane-containing coating. Both the freshly
coated substrate and the rinse water were at room temperature.
Rinsing was necessary to prevent the entrainment of substances from
the pretreatment solution into the downstream paint bath. The
freshly rinsed coated substrate was then dipped immediately in the
cathodic dip paint, so that no further drying could occur. However,
the coated sheets of the comparative examples were dried for 5
minutes at 120.degree. C. in the drying cabinet immediately after
rinsing, but the examples according to the invention were coated
immediately thereafter by immersion in a cathodic dip coating
without intermediate drying.
The visual test of the coatings can be performed significantly only
with the coatings on steel because of the interference colors and
this allows an evaluation of the uniformity of the coating. The
coatings without any complex fluoride content are extremely uneven.
Coating with titanium and zirconium complex fluoride has
surprisingly proven to be much more uniform than if only if one of
these complex fluorides had been applied. Addition of
nitroguanidine, nitrate or nitrite also improves uniformity of the
coating. In some cases, the layer thickness would increase with the
concentration of these substances.
TABLE-US-00002 TABLE 2 Compositions of baths in g/L based on solids
contents, or in the case of silanes, based on the weight of the
hydrolyzed silanes; residual content: water and in most cases a
very small amount of ethanol; process data and properties of the
coatings Example/Comparative example CE 1 E 1 CE 2 E 2 CE 3 E 3 CE
4 E 4 CE 5 E 5 CE 6 E 6 CE 7 E 7 CE 8 E 8 CE 9 E 9 Organo- 0.2 0.2
0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.1 0.1 0.3 0.3 0.2 0.2 0.- 2 0.2
functional silane A H.sub.2TiF.sub.6 as Ti -- -- 0.2 0.2 -- -- 0.2
0.2 0.2 0.2 0.1 0.1 0.3 0.3 0.2 0.2 0.2 0.2 H.sub.2ZrF.sub.6 as Zr
-- -- -- -- 0.2 0.2 0.2 0.2 0.2 0.2 0.1 0.1 0.3 0.3 0.4 0.4 0.2 0.2
Mn -- -- -- -- -- -- -- -- -- 0.3 0.3 -- -- -- 0.3 0.3 -- --
Silylated epoxy -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 1.0
1.0 polymer pH 10.5 10.5 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 Layer
weight 10-20 10-20 20-50 20-50 20-50 20-50 20-50 20-50 20-60 20-60
10-40 10-40 - 30-80 30-80 30-80 30-80 50- 50- in mg/m.sup.2 100 100
from silanol and metal BMW cross-cut test: grade Steel 4 3 5 5 3 2
2 1 1 0 2 1 1 1 1 0 1 1 E-zinc on steel 3 3 4 3 4 3 1-2 1 1 0 1 1 1
1 1 1 0 0 Galvanized 2 2 4 3 4 3 1 0 0 0 1 0 0-1 0-1 0-1 0 0 0 zinc
on steel Al 6016 2 2 2 2 2 2 1 1 1 0 2 1 1 1 1 0 1 1 Galvanneal
.RTM. 1 1 1 1 2 1 1 0 1 0 1 0 0 0 0 0 0 0 Ten cycles of VDA mm,
migration beneath coating: Steel 8 6 7 5 4 3 3 2.5 2 1 3.5 2 1.5
1.5 1.5 <1 2.5 2 E-zinc on steel 5 4 3 2.5 4 4 2 1 1 <1 3 1.5
1.5 1 1 <1 1 <1 Galvanized 4 4 2.5 2 3.5 3 <1 <1 <1
<1 1.5 1 1 1 1 <1 <- 1 <1 zinc on steel Galvanneal
.RTM. 2 2 2 1 1.5 1.5 <1 0 <1 <1 1 1 <1 <1 <1-
<1 0 0 Rock fall according to VDA loading, grade Steel 5 5 4 4 4
3 2-3 1 1 1 2 2 2 1 1-2 1 1 0-1 E-zinc on steel 5 4 3 2 4 3 2 1 1 1
2 1 1-2 0 1 0 1 0-1 Galvanized 5 4 3 2 4 3 1 0 1 0 1 1 1 0 1 0 0 0
zinc on steel Galvanneal .RTM. 4 4 2 2 3 2 1-2 0 1 0 1 0-1 0 0 0 0
0 0 Salt spray test 1008 hours: Steel 7 6 4 4 3.5 3 2 1.5 1.5 <1
2.5 2 1.5 <1 1.5 <1 1 1 CASS test mm migration Al 6016 6 6
3.5 3 3.5 3 2.5 2.5 1.5 1 2.5 2 1.5 1 1.5 1 1.5 1 E = Example; CE =
Comparative example
If the various metallic surfaces that were coated are considered as
a whole, all the examples show a significant improvement in the
properties of the aqueous silane-based composition in comparison
with the respective comparative example, wherein the same bath
composition was applied in one case with subsequent drying (as
comparative example CE) and in one case without subsequent drying
(as example E according to the invention). The examples presented
here are then examples according to the invention if they are
utilized with this composition over the entire process sequence up
to electro-dip coating on components using wrap-around.
It was surprising that this improvement, which actually brings only
a limited improvement, in particular in cases where the coating
results are already good, is systematically improved by not drying
after application of the aqueous composition. Therefore, by
omitting the drying, it is surprisingly possible to achieve a
significant improvement, which is almost independent of the
chemical composition of the aqueous bath. It was initially
surprising that this improvement occurred with the solutions
containing only silane as well as with the solutions containing
silane and complex fluoride and/or optionally also manganese ions.
It is therefore assumed that a similar steady improvement from
drying to nondrying also occurs with solutions having a similar
composition or with solutions based on silane or based on silane
and complex fluoride and containing a few different substances.
When more substances are present and when the low contents are
higher, the corrosion resistance and paint adhesion may be better,
as long as an optimum that might have occurred is not exceeded.
The layer weight varies not only according to the amounts of the
individual components of the aqueous solution but also according to
the type of the respective metallic surface which is coated. By
selecting the bath components and their amounts, a very definite
improvement in corrosion resistance and paint adhesion can thus be
achieved on the whole.
The bath compositions all proved to be stables in the very short
use time and could be applied well. There were no differences in
behavior, in the visual impression or in the test results among the
various examples and comparative examples that could be attributed
to the treatment conditions, for example, application by spraying,
dipping or roll coater treating. The resulting films are
transparent and almost all of them are largely uniform. They do not
show any pigmentation of the coating. The resulting films are
transparent and almost all of them are largely uniform. The
structure, gloss and color of the metallic surfaces appear to be
only slightly altered by the coating. In the case of a titanium
and/or zirconium complex fluoride content, iridescent layers are
formed on steel surfaces in particular. The combination of several
silanes has not yet resulted in any further significant improvement
in corrosion protection in the experiment. However, this cannot be
ruled out. In addition, an H.sub.3AlF.sub.6 content was found on
aluminum-rich metallic surfaces due to corresponding reactions in
the aqueous composition. However, the combination of two or three
complex fluorides in the aqueous composition has surprisingly
proven to be extraordinarily successful.
The layer thickness of the coating produced in this way--even
depending on the method of application, which was initially varied
in separate tests--is in the range of 0.01 to 0.16 .mu.m, usually
in the range of 0.02 to 0.12 .mu.m, often as little as 0.08 .mu.m,
and it is definitely greater when an organic polymer was added.
Based on the development of zinc-manganese-nickel phosphating of
vehicle bodies, which had been developed over a period of several
decades, such phosphate layers produced today are of an extremely
high quality. Nevertheless, contrary to expectation, it was also
possible to achieve the same high-quality results even with the
coatings containing silane, although greater efforts were necessary
in this regard, even with the aqueous compositions containing
silane that have been in use for only a few years.
The corrosion prevention grades in the cross-cut test according to
DIN EN ISO 2409 after storage for 40 hours in 5% NaCl solution,
corresponding to BMW specification GS 90011, were from 0 to 5,
where 0 indicates the best value. In the salt spray condensed water
alternating tests over 10 cycles according to the VDA test sheet
621-415 with a varying corrosion load between the salt spray test,
the condensation water test and a drying pause, migration beneath
the cut was measured on one side, starting from the scratch and
reported in mm, where the under-migration was to be as low as
possible. In the rock fall test according to DIN 55996-1, the
coated sheets are bombarded with steel scrap following the VDA
alternating load test for 10 cycles, as described above. The damage
pattern is characterized by characteristic values from 0 to 5,
where 0 indicates the best results. In the salt spray test
according to DIN 50021 SS, the coated sheets were exposed to a
corrosive sodium chloride solution by spraying for up to 1008
hours. Then the migration was measured in mm for the scratch, where
the scratch was produced down to the metallic surface using a
standardized gouge and where the migration beneath the film should
be as minor as possible. In the CASS test according to DIN 50021
CASS, the coated sheets made of an aluminum alloy are exposed to a
special corrosive atmosphere by spraying for 504 hours. Then the
migration from the scratch is measured in mm and should be as small
as possible.
Additional experiments on vehicle body elements have shown that the
electrochemical conditions of the CDC bath could possibly be
adapted slightly to the different type of coating but otherwise the
excellent properties observed in the laboratory experiments on
sheet metal can also be applied to vehicle body elements in an
industrial environment.
The influence of additives on the spray water was investigated in
additional experiments.
TABLE-US-00003 TABLE 3 Comparison of coating methods with and
without the use of at least one surfactant and optionally
additional additives in the rinse water to improve the electro-dip
coating results Example/Comparative example ("a" stands for the
wet-wet process) CE 10 E 10 CE 11 E 11 CE 12 E 12 E 13 E 14
Additives to the rinse water: Total surfactant content in g/L --
0.2 -- 0.2 -- 0.2 0.2 0.2 + 0.2 Added surfactant mixtures -- A -- A
-- A B A + B Additional additives and content -- -- 1) 0.1 1) 0.1
2) 0.005 2) 0.005 -- -- in g/L Cross-cut after 240 hours in the KK
5 2 3 2 1 1 0 0 test: grade Salt spray test 1008 h in mm 4.5 2.3
4.0 2.8 3.0 3.0 2.5 2.5 Visual impression of the beading of good
good good good good good very very the rinse fluid good good Visual
impression of the layer good good good good good good good good
containing silane after rinsing Layer thickness CDC in .mu.m 43.7
41.9 40.3 38.3 39.8 38.4 37.7 37.5 Layer thickness fluctuations of
the 3.0 1.5 1.6 1.0 1.7 1.3 1.6 0.5 CDC .DELTA.d in .mu.m Visual
homogeneity of the CDC very faint heavy faint heavy faint faint
faint layer with respect to streaks heavy streaks streaks streaks
streaks streaks streaks streaks streaks Visual: evenness of the CDC
layer very somewhat somewhat very somewhat somewhat almost almost
uneven uneven uneven uneven uneven uneven even even
Examples/Comparative example CE 15 E 15 E 16 E 17 E 18 Additives to
the rinse water: Total surfactant content in g/L -- 0.2 0.2 0.2 0.2
+ 0.2 Added surfactant mixtures -- C D A A + B Visual impression of
the flow of the rinse good good very good very fluid good good
Visual impression of the layer containing good good good good Good
silane after rinsing Visual: homogeneity of the CDC layer heavy
faint faint faint faint with respect to streaks streaks streaks
streaks streaks streaks Visually: evenness of the CDC layer very
somewhat somewhat somewhat almost uneven uneven uneven uneven even
Center layer thickness of CDC, outside, 16 18 19 19 20 .mu.m Center
layer thickness of CDC, inside, .mu.m 5 16 17 17 19 Fluctuations in
layer thickness of the CDC 11 2 2 2 1 .DELTA.d in .mu.m between the
inside and the outside as a measure of throwing power E = Example
CE = Comparative example
All examples and comparative examples E 10 to E 18 and CE 10 to CE
12 as well as CE 15 to CE 18 were used in the wet-on-wet method
with and without addition of a surfactant to the water after-rinse
following the aqueous silane-based pretreatment and before
immersion in the same electro-dip paint used for the manufacturing
series. The compositions of the examples E 10 to E 18 and
comparative examples and CE 10 to CE 12 and CE 15 to CE 18 were
produced in the same way as the other examples and comparative
examples and were used, except that only sheets of cold-rolled
steel (CRS) were used in the second series and sheets of hot-dip
galvanized steel were treated in the third series, and the sheets
treated with the silane-containing composition were stored in room
air at room temperature for 5 minutes to 30 minutes after rinsing
before they were coated with a commercially available cathodic dip
coating (electro-dip paint, e-coat, CDC) by immersing at 250 V
(second series) or at 240 V (third series).
However, a slightly different type of cold-rolled steel was used
than in the first series for the experiments according to Table 2
(=first series). For the examples E 10 to E 14 and comparative
examples and CE 10 to CE 12 (second series), however, a different
electro-dip paint was used than that used for examples E 15 to E 18
and comparative examples CE 15 to CE 18 (series 3). An electro-dip
paint of generation 6, MC3 of PPG, was used for the latter. The
layer thicknesses of the electro-dip paint were measured using the
VDA method.
The half-hour waiting time simulates the cycle time of vehicle
bodies coated in this way until the vehicle body is immersed in the
CDC pool. The silane-containing coatings dry somewhat superficial
here but not completely. The silane pretreatment of these examples
and comparative examples is based on the compositions of example E
8 and comparative example CE 8, wherein aqueous silane-based
pretreatment compositions, such as those in E 8 and CE 8, were used
in the third series, except that they also contained 0.001 to 0.10
g/L Cu and 0.1 to 1 g/L Zn plus optionally also traces of Al and
small amounts of Fe. The pH was also set at 4. The deionized water
for the after-rinse was prepared with the addition of at least one
surfactant in the examples according to the invention, where the
surfactant or the surfactant mixture was added in the form of an
aqueous solution. The surfactant mixture A contained a nonionic
surfactant based on a fatty alcohol polyglycol ether. The
surfactant mixture B contained a different type of nonionic
surfactant and a solubilizer. The surfactant mixture B proved to be
especially suitable for beading of the rinse water. The surfactant
mixture C contained a nonionic surfactant based on an alkylamine.
The surfactant mixture D contained a nonionic surfactant and a
cationic surfactant. Additive 1) was a water-soluble diphosphonic
acid with a longer alkyl chain. Additive 2) was a water-soluble tin
compound.
All the CDC layers of a series were applied at the same voltage,
even if this resulted in great differences in layer thickness.
Fundamentally, the CDC layers of the second series were slightly
too thick. The layer thicknesses were formed not only according to
the electric conductivity of the pretreated substrate but
apparently also to a great extent depended on the quality of the
remaining pretreatment layer, which evidently differed in
uniformity due to the different rinse compositions. The conditions
were selected, so that inhomogeneities in the electro-dip paint
were readily visible and a differentiation in the quality of the
CDC layer was possible.
The additional investigations were performed on pretreated rinsed
and CDC-coated sheet metal but they were different than in the
first series of examples and comparative examples without the
additional paint layers of a typical automotive paint structure:
the corrosion resistance was determined in the salt spray test
according to DIN EN ISO 9227 over a period of 1008 hours, and the
paint adhesion was determined according to the cross-cut test
method after a 240-hour constant climate test according to DIN EN
ISO 6270-2 and according to DIN EN ISO 2409. In both test methods,
the smaller values are better values.
On the one hand, a surprisingly strong correlation of the results
with respect to corrosion resistance, paint adhesion CDC layer
thickness and presumed homogeneity of the CDC layer as well as a
great dependence of the results on rinsing with and without
surfactant was revealed, wherein additives to the rinse water
containing surfactant to some extent also yielded a further
improvement. On the other hand, it was found that the homogeneity
of the CDC layer is better, the smaller the resulting CDC layer
thickness. Although the CDC layers of examples E 13 and E 14 were
the thinnest in this series, these coated metal plates nevertheless
had a much better corrosion resistance than the thicker CDC layers.
The differentiation in quality with regard to paint adhesion is
also surprisingly strong over the total possible range of grades
from 5 to 0.
It has surprisingly been found that the quality of the silane-based
pretreatment coating and the composition of the water for rinsing
after the silane pretreatment had a substantial effect on the
quality of the paint layers applied subsequently.
It was surprising that addition of at least one surfactant would
have a strong effect on the subsequent coating with the electro-dip
paint despite the comparatively low surfactant content in the rinse
water and due to a very thin surfactant film which is even
monomolecular under some conditions and is thereby produced and
that the addition of at least one surfactant in the after-rinse
would have strong effect on the interface between the silane
pretreatment coating and the electro-dip coating as well as on the
layer formation of the electro-dip coating. The electro-dip paints
selected in the second and third series are of a particularly high
quality and it is known that they can be processed especially
uniformly.
Nevertheless, the unevenness in the electro-dip coating layer was
so great in comparative example CE 11a that it must be assumed that
marks would be visible up to the top coat in the subsequent coating
with the paint layers that are typically used in automotive
engineering. On the other hand, it has been observed in similar
studies that clearly visible striations were formed in coating
large-area vehicle body elements when they were rinsed without
addition of a surfactant, but these striations could be prevented
by adding a surfactant. A smoother CDC layer could be produced with
the surfactant additive in the rinse liquid and would then in turn
be partially responsible for the fact that even more uniform,
smoother paint layers with fewer defects could be formed on the CDC
layer. The throwing power of the paint in electro-dip coating was
surprisingly also influenced to a great extent.
In the after-rinse following the silane pretreatment with water
alone, inhomogeneities in the electro-dip paint that was
subsequently applied or observed repeatedly despite the adequate in
some cases repeated rerinsing and despite rerinsing at least once
with deionized water.
In additional experiments not presented here in detail, it was also
determined that fundamentally any surfactant can be added, wherein
nonionic surfactants in particular are preferred, but it is
necessary to select low-foaming surfactants or those with little or
almost no foam production and/or surfactant-containing mixtures for
rerinsing by spraying and these mixtures may additionally contain,
for example, a foam suppressant and/or a solubilizer and may have a
minor, very minor or almost no tendency to foam, for example, in
spray processes when used individually or in any combination. The
nonionic surfactants are advantageously selected from linear
ethoxylates and/or propoxylates, preferably those with alkyl groups
of 8 to 18 carbon atoms. The latter also includes the surfactants
A, B and D. With such a combination of surfactants, the wetting and
foam suppressing properties can be optimized at the same time but
surprisingly a plurality of properties of the electro-dip paint and
electro-dip coating have proven to be advantageously subject to
influence by such a combination of surfactants.
On a zinc-rich metallic substrate in particular, the quality of the
silane pretreatment and the type of after-rinse with water have a
very strong effect on the homogeneity or inhomogeneity of the
electro-dip coating (e-coat, CDC) and consequently also on the
subsequent paint layer such as the base coat (filler as color
medium) and the subsequent top coat (clear enamel). In the case of
rinse water containing no added surfactant, it has been found that
inhomogeneities in the electro-dip paint such as streaks are hardly
avoidable. Streaks and other inhomogeneities as well as unevenness
then subsequently easily and frequently lead to plastic marks in
the following paint layers. Basically there should not be any
plastic marks in the base coat or in the top coat of vehicle bodies
for automobiles because these usually necessitate intense
mechanical reworking and repainting. If the paint layers in
reworking are removed too greatly, e.g., in reworking, for example,
down to or even into the metallic substrate, then a pretreatment
should also be applied before applying the first paint layer, for
example, a pretreatment composition based on at least one silane or
based on at least one silane with a titanium and/or zirconium
compound and/or with an organic polymer. Such reworking not only
causes problems in the work sequence but also causes substantial
costs in particular due to the manual labor.
If at least one surfactant has been added to the rinse water and if
the silane pretreatment has been processed well in the normal way,
inhomogeneities were not observed anywhere in the electro-dip
coating in any of the experiments and plastic marks were not found
in any of the following paint layers. Plastic marks refer to
inhomogeneities in the top paint layer, which are more or less
distinctly visible to the naked eye due to height differences in
the paint surface in particular. Only if the pretreatment
composition itself was already extremely inhomogeneous were
definitely inhomogeneous electro-dip coating layers formed even
under extreme conditions after the after-rinse with rinse water
containing surfactant and, following that, paint layers with only
minor plastic markings were obtained.
The electro-dip-coated substrates whose aqueous silane-based
pretreatment coating was rinsed with water containing a surfactant
showed a definitely better paint throwing ability than the
electro-dip-coated substrates rinsed with water that did not
contain a surfactant.
Metallic components can be electro-dip coated with good results
using the coating method according to the invention, even if
problems had already occurred before the silane-based pretreatment,
the water rinse contains no surfactant and no iron-containing
treatment is performed before the silane-based pretreatment.
Alternatively or in addition to the procedure with the aqueous
rinse containing surfactant, an aqueous treatment with an iron
compound dissolved in water can be performed before the
pretreatment with the silane-based composition.
In a new series of experiments, a further improvement in the
application of the cathodic electro-dip paint to metallic surfaces
containing zinc was found in examples 20 to 23 and in similar
process variants in comparison with the procedures using a water
rinse with or without a surfactant content. This improvement was
achieved due to the fact that with an otherwise similar treatment
sequence and similar treatment conditions as in the examples listed
in Table 3, in which the electro-dip coating layer often has a 5 to
15% smaller layer thickness even when the temperature is constant
and the voltage is kept constant. For cleaning the sheet metal
prior to the silane-based pretreatment, a two-step cleaning process
was utilized in which the sheet metal was first sprayed and then
was dipped. When two content values are listed in Table 4, the
content on the left is based on the spray process and the content
on the right is based on the dipping operation if different
contents were utilized. In this procedure the electro-dip coating
layer was applied by using silane-based pretreatment compositions
in comparison with zinc phosphate-based pretreatments with a lower
voltage, so the throwing power of the electro-dip coating paint is
also lower accordingly. It is therefore desirable to be able to use
a voltage higher than 250 V, for example, without exceeding a layer
thickness of the dried and baked electro-dip coating layer of 20
.mu.m, for example. In these examples an ideal layer thickness of
the dried and baked electro-dip enamel layer on the outside was
obtained by using a voltage of approx. 250 V in electro-dip coating
without employing the process steps according to the invention. The
reduction in this layer thickness despite the use of a voltage of
250 V in electro-dip coating indicates the possibility of using a
higher voltage which then also leads to a higher throwing power.
The surfactant E added here is a nonionic surfactant based on an
alkyl ethoxylate with one alkyl group and with end group capping in
which a cationic compound was also added. The pH of the cleaning
agent was in the range of 10 to 11. In cleaning in examples 20 to
23, a gluconate and/or a heptonate was added as a complexing agent
in the total amount indicated there. Furthermore the cleaning agent
contained at least one alkali compound which served to adjust the
pH. Other variants that were not listed in detail in Table 4 relate
to optional additional additives of boric acid or silicate as well
as additional variation of all the cleaning agent ingredients, but
all these process variants led to the same or similar results. In
comparison with all these examples according to the invention, no
cleaning step containing Fe was performed in comparative example
19, nor was there a rinse using a surfactant.
It has now been found that the use of an aqueous composition
containing iron before application of the silane-based pretreatment
composition permits an increased voltage in electro-dip coating for
the production of a dried and backed electro-dip coating layer of
20 .mu.m, for example. The voltage used here was often 5 to 15%
higher, for example, 260 to 290 V. It was also found here that the
throwing power achieved was also approx. 5% to 15% improved based
on the increased voltage. Preliminary results also indicate
improved paint adhesion and improved corrosion resistance for these
variants according to the invention.
TABLE-US-00004 TABLE 4 Comparison of coating methods with and
without Fe-containing additive in two-step cleaning and with and
without the use of at least one surfactant in the rinse water to
improve the electro-dip coating Addition in g/L (cleaning: left
equal first spraying; right equal Examples/Comparative example
subsequent dipping) CE 19 E 20 E 21 E 22 E 23 Additives in
cleaning: Surfactant E + cationic compound 2.0/3.0 2.0/3.0 2.0/3.0
2.0/3.0 5.0/8.0 Water-soluble Fe.sup.2+ compound -- -- -- sulfate
-- Amount of Fe.sup.2+ additive 0 0 0 0.080 0 Water-soluble
Fe.sup.3+ compound -- nitrate nitrate nitrate nitrate Amount of
Fe.sup.3+ additive 0 0.056/0.084 0.056/0.084 0.056/0.084
0.056/0.084 Carboxylic acid(s) additive 0 0.8/1.2 0.8/1.2 0.8/1.2
0.8/1.2 Additives to rinse water: Total surfactant content in g/L 0
0 0.2 0 0 Surfactant added -- -- E -- -- Visual impression of the
flow of good Good very good good rinse fluid on the
silane-containing good layer Visual impression of the silane- good
Good good good good containing layer after rinsing Visual:
homogeneity of the CDC heavy faint faint faint faint layer with
respect to streaks streaks streaks streaks streaks streaks Visual:
evenness of the CDC very slightly almost slightly slightly layer
uneven uneven even uneven uneven Average layer thickness of CDC
19.5 17 16 16 18 on the outside, .mu.m Average layer thickness of
CDC 7 15 14 14 17 on the inside, .mu.m Fluctuations in layer
thickness of 12.5 2 2 2 1 the CDC, .DELTA.d in .mu.m between the
inside and the outside as a measure of throwing power E = Example
CE = Comparative example
* * * * *